Field of the Invention
[0001] The invention relates to a digital wireless communication system. In particular,
the invention relates to cordless telephones and cellular networks.
Background
[0002] A common type of wireless communication is the communication which occurs between
a cordless telephone handset and its associated base unit within a limited distance
range around the user's home or business. Cordless telephones typically operate over
a radio frequency (RF) portion of the spectrum set aside for general public use. Also,
the power of the cordless phone signal is lower than other communication signals,
because the signal needs to only be transmitted between the cordless handset and the
associated base unit within the home or business of the user. Therefore, there is
no user license from the Federal Communications Commission (FCC) required to operate
a cordless telephone. Ultimately the communication is carried from the associated
base unit along a landline on the public telephone network to the connecting party;
therefore the cost of the telephone call is regulated by the LEC which owns the public
switched telephone network (PSTN).
[0003] Another method of wireless communication is a regional cellular communication network
which is operated by a cellular operator to enable the transmission of voice and data
from a mobile station to a cellular base station over a specific band of frequencies,
e.g., 824-849 MHz and 869 894 MHz, under license by the FCC. The bands are generally
broken up into transmission channels and reception channels which each employ different
bands of frequencies in the cellular spectrum. Cellular transmissions from the base
station to the mobile station occupies the spectrum between 824 and 849 MHz with each
transmission channel occupying about 30 KHz Cellular reception from the mobile stations
to the base stations generally occupy the spectrum between 869 and 894 MHz with each
reception channel occupying about 30 KHz. As is well known to those of ordinary skill
in the art, each of the transmission and reception bands are divided between two cellular
service providers in each market and are referred to as "A" and "B" bands. Thus, each
provider operates four hundred and sixteen pairs of transmission and reception frequency
channels on which to provide service. Twenty-one of the four hundred and sixteen frequency
channels pairs are ordinarily used as control channels to send control signals from
the base station to the mobile station, thus only three hundred and ninety-five channels
are actually available to transmit calls between the cellular base station and mobile
station. The cellular service provider enlists subscribers who are authorized to communicate
via the regional cellular network. Each subscriber must purchase a mobile station
or handset which is capable of communication with the regional cellular network. The
handset, at the time of manufacture, is assigned an electronic serial number (ESN).
The ESN is generally stored in the permanent memory, such as an EEPROM, in the handset.
The subscriber registers the mobile station with the regional cellular network and
the mobile station is assigned a mobile identification number (MIN) by which the mobile
station can be accessed. As the price of mobile stations decreases and the cost of
air time decreases, the number of users that subscribe to regional cellular networks
is increasing.
[0004] Recently, handsets have been disclosed which are capable of switching between communication
with a cellular network and with an RF cordless telephone unit. Once the handset is
in the proximity of the cordless telephone unit, the telephone unit is capable of
receiving calls from both the public switched telephone network (via the RF cordless
telephone unit) and the regional cellular network. Since the cellular and RF cordless
communication systems utilize different frequency bands for communication, a handset
that can communicate with both cellular and RF cordless base stations requires some
significant additional hardware and software. In practice, a handset that can communicate
with both types of base stations requires one transceiver that can communicate with
cordless frequencies and one transceiver that can communicate with cellular frequencies
as well as separate interface hardware between each transceiver and the main handset
controlling hardware. Further, the main handset controlling hardware must be able
to recognize and communicate with the different communications protocols required
to communicate with the RF cordless telephone base station and with the cellular networks.
The additional hardware required to communicate with both base stations increases
the size and the weight of the handset. Further, the additional hardware increases
the cost of the handset in a highly price-competitive market.
Summary
[0005] The preferred embodiment of the present invention comprises a cordless cellular base
system. A cordless cellular base station is capable of communicating with a cellular
network compatible mobile unit, also referred to as a mobile station herein. The cordless
cellular base station, also referred to as a subregional basestation, is preferably
connected to a landline on a public switched telephone network and is assigned a landline
number or phone number. The mobile station is registered with a cellular network and
is assigned a mobile identification number. Advantageously, the mobile station is
capable of communication with both a conventional regional cellular base station and
to the cordless cellular base station utilizing the same cellular frequency range
and communications protocol. When the mobile station is communicating with the cellular
network, it is referred to as being in the regional cellular service mode. When the
mobile station is communicating with the cordless cellular base station, it is referred
to as being in cordless cellular telephone landline service mode.
[0006] The mobile station of the present invention advantageously communicates with the
cordless cellular base station and with the regional cellular base stations of the
cellular network utilizing the same frequency range and the same communications protocol.
In a preferred embodiment, the communications protocol that is utilized is compliant
with the IS-136, parts one and two, air interface standard which is hereby incorporated
by reference in its entirety. The IS-136, parts one and two, standard is available
from the Telecommunications Industry Association (TIA), Engineering Dept., 2001 Pennsylvania
Avenue, N.W., Washington, D.C. 20006. This standard provides in part for TDMA (time
division multiple access) digital communications and is well known to those of skill
in the art. The IS-136 standard is designed to ensure compatibility between cellular
mobile telecommunication systems so that a mobile station can obtain service in any
cellular system manufactured in accordance with the standard. Since the mobile station
communicates with the cordless cellular base station and with the regional cellular
base stations of the cellular network utilizing the same frequency range and the same
communications protocol, the mobile station may be manufactured using similar hardware,
such as a digital transceiver, and similar software to communicate with both the cordless
cellular base station and the cellular network. Therefore, the overall size and the
weight of the mobile station is not increased compared to conventional cellular telephones
which are compatible with the IS-136 standard. Further, by reducing the amount of
additional hardware and additional software necessary, the cost of the mobile station
of the preferred embodiment is not much higher than conventional IS-136 compliant
mobile stations. The cordless cellular base station is able to communicate with the
mobile station and act as a conduit between the mobile station and the public switched
telephone network. Further, despite the fact the mobile station is IS-136 compliant
and can communicate with both analog and digital regional cells, the mobile station
preferably communicates with the cordless cellular base station utilizing a digital
control channel and corresponding digital traffic channels. By utilizing a digital
channels, rather than analog and digital channels for communication with the mobile
station, the hardware and software required to operate the cordless cellular base
station is further reduced and thus the manufacturing costs are reduced.
[0007] In one aspect of the present invention, in order to maintain a secure system, the
cordless cellular base station must first register with the cellular network before
its operation is enabled. In a preferred embodiment, the cordless cellular base station
is not operational without the network authorization, as the cellular network provides
the cordless cellular base station with certain operating parameters, such as a list
of authorized frequencies for its operation. After the network authorization procedure
is complete, the cordless cellular base station enables registration of mobile stations.
In the preferred embodiment, once a mobile station receives registration privileges
with a particular cordless cellular base station, the mobile station automatically
registers with the cordless cellular base station when the mobile station comes into
proximity with the cordless cellular base station. As the number of cordless cellular
base station users increases it becomes more likely that at least some cordless cellular
base stations will be operating in close proximity to one another. With base stations
present in adjoining houses, for example, it is not desirable to enable automatic
registration for all mobile station users that come into proximity with a cordless
cellular base station, because it is possible for one neighbor to inadvertently automatically
register with another neighbor's cellular base station. Advantageously, the automatic
registration feature of the present invention allows the cordless cellular base station
to restrict automatic registration to those users who have been previously pre-registered
with a particular cordless cellular base station. By requiring preregistration, before
automatic registration occurs, accidental automatic registration with a nearby cordless
cellular base station is prevented while still providing the convenience of automatic
registration for frequent users. In addition, the mobile station will not attempt
to automatically register with a cordless cellular base station unless it has previously
registered with that cordless cellular base station and knows on which channels to
look for the cordless cellular base station.
[0008] In another aspect of the present invention, the cordless cellular base station maintains
a cordless cellular base station registration list in a semipermanent portion of memory
which stores the mobile system identification number of the mobile stations which
have been previously been granted registration privileges with the cordless cellular
base station. For each entry, the cordless cellular base station registration list
stores a status record that indicates the state of the mobile station with respect
to the cordless cellular base station and the mobile station identification number.
Preferably, there are three states of a mobile station with respect to the cordless
cellular base station which are referred to as the: "standby", "active" and "dormant"
states. The dormant state indicates that the mobile station which has previously registered
with the cordless cellular base station is not currently registered with the cordless
cellular base station. The standby state indicates that the mobile station is currently
registered with the cordless cellular base station and is not currently on a call,
i.e., the mobile station is "standing by" waiting to receive or place a call through
the cordless cellular base station. The active state indicates that the mobile station
is registered with the cordless cellular base station and is currently on a call which
is being controlled by the cordless cellular base station. In a preferred embodiment
the status of up to ten mobile stations can be monitored by the cordless cellular
base station.
[0009] In another aspect of the present invention, when a mobile station which is not presently
involved in a call comes within range of a cordless cellular base station with which
it has previously registered, in accordance with the preferred embodiment, it automatically
switches from regional cellular service mode to cordless telephone landline service
mode without user intervention. Once the mobile station has confirmed with the cordless
cellular base station that the mobile station has switched to cordless landline service
mode, the cordless cellular base station communicates with the cellular network to
provide a location update message. If the mobile station has a call in progress, the
mobile station waits for the call to be completed before it is switched to cordless
telephone landline service mode and sends the call forwarding update message.
[0010] Once the cellular network receives the call forwarding update, the cellular network
routes all calls to the mobile station's mobile identification number to the landline
number associated with the cordless cellular base station. In addition, while the
mobile station remains within range of the cordless cellular base station, all calls
placed from the mobile station are sent through the cordless cellular base station
to the associated landline. In the preferred embodiment there is no hand-off of telephone
calls between the regional cellular network and cordless cellular base station environments.
For example, if a call is initiated via the cordless cellular base station and the
mobile station is moved to an area outside of the cordless cellular base stations
range, the call is disconnected instead of being transferred to the cellular network.
In an alternate embodiment, handoff of telephone calls between the regional cellular
network and cordless cellular base station environments is enabled. For example, if
a call is initiated via the cordless cellular base station and the mobile station
moves to an area outside of the cordless cellular base station's range, the call is
automatically transferred from the cordless cellular base station and its associated
landline to the cellular network. The cellular network then routes the call through
the cellular base station and a hand-off is performed to the user's mobile station
as is performed in a conventional cellular system.
[0011] By communicating with the cellular network, the cordless cellular base station is
advantageously able to inform the cellular network where to route telephone calls
for the mobile station's identification number when the mobile station is registered
with the cordless cellular base station ensuring that the mobile station user will
always receive telephone calls for its mobile station identification number regardless
of the mode of operation of the mobile station.
[0012] Typically, when the mobile station severs contact with the cordless cellular base
station, the cordless cellular base station sends a network forwarding cancellation
message to the cellular network to cancel the forwarding of calls for the mobile station
identification number to the landline number associated with the cordless cellular
base station. The cordless cellular base station is informed during an initial authorization
message which types of registration/deregistration activities for which the network
wants to be informed. Some examples of types of deregistration events for which the
network may want to be contacted are: when the mobile station is turned off, i.e.,
a power down deregistration or due to a manual cancellation of the cordless service
mode, i.e., forced deregistration. When the mobile station severs contact with the
cordless cellular base station for reasons other than powering off, the mobile station
typically registers with the local regional cellular base station of the regional
cellular network. Once the mobile station is registered with the regional cell, calls
to the users mobile identification number are directly routed by the cellular network
to the mobile station.
[0013] In another aspect of the present invention, the cordless cellular base station can
process up to two active mobile stations at the same time. When two mobile stations
are listed as active, the cordless cellular base station bridges the audio signal
for the two mobile stations together such that each of the mobile stations is acting
like an extension on a normal landline. In a first embodiment, each mobile station
receives a voice signal which is a summation of the voice signals from the caller
on the landline and from the other mobile station. In a second embodiment, the cordless
cellular base station compares a voice signal from one mobile station with the voice
signal from the caller on the land line and whichever is loudest is sent to the other
mobile station. The voice signals from each of the mobile stations are summed together
and sent to the landline. Thus, the landline caller hears a summation of both mobile
stations speaking while each mobile station only hears whichever signal is louder,
the other mobile station or the caller on the landline. In a third embodiment, the
cordless cellular base station uses a detector to determine which of the signals from
the mobile stations is the loudest and sends the loudest received signal to the caller
on the landline. The users of the mobile stations are able to listen to the voice
of the party on the landline; however, they are unable to hear what is being said
by the user of the other mobile station.
[0014] The cordless cellular base station is designed to operate in the residential home
or small office environment. This active RF environment can be potentially very noisy
because there may be no dedicated frequency spectrum allocated for the cordless cellular
base station operation coupled with the fact that the frequency usage is not explicitly
coordinated with the regional cellular network planning. The cordless cellular base
station has to co-exist in the same cellular band used by the regional cellular network
and views the regional cellular network as a source of background interference. The
cordless cellular base station attempts to avoid the potential interference by the
cellular network by choosing frequencies which, as far as the cordless cellular base
station can determine, are not being used by nearby regional cells or by other nearby
cordless cellular base stations.
[0015] In another aspect of the present invention, the cordless cellular base station implements
an avoidance mechanism which scans the frequencies in the cellular band and determines
the best and next-best cellular frequencies for communication with the cellular network
at all times. The cordless cellular base station periodically takes received signal
strength (RSS) measurements for each of the authorized frequencies of the cordless
cellular base station and word error rate (WER) measurements on the current operational
frequency when a call is in progress, which are measurements known to those of skill
in the art. The cordless cellular base station translates the RSS measurements into
a score increment or decrement value based upon a stored score increment table. After
each measurement, the current score increment/decrement value adjusts the previous
score value. The score for a frequency is a measure of the amount of noise plus interference
at a given frequency, thus the score itself is a measure of the potential of interference
if this channel were selected rather than the actual interference occurring on the
channel. Therefore, throughout this document any discussion of the measurement of
the interference on a channel should be interpreted as the measurement of the potential
interference on this channel, if the channel was selected for operation. Thus, the
interference score represents the potential interference that would be encountered
on that frequency, with a higher score representing more interference, and a lower
score representing lower interference. In the absence of interference, the score value
will gradually decay towards zero as more measurements are made.
[0016] The cordless cellular base station uses the interference score measurements in making
the choice of an operating frequency. By selecting a frequency from those with the
lowest interference scores, and by using appropriate channel abandonment thresholds
described below, the cordless cellular base station attempts to avoid transmitting
on any frequency which is already in use nearby the public or private cellular network
or by other cordless cellular base stations within range. Preferably, the cordless
cellular base station selects for its initial operational frequency, the frequency
with the lowest interference score. The cordless cellular base station 10 randomly
selects for its backup frequencies, a specified number of downlink frequencies whose
scores are below a high threshold value (Ht). Depending upon whether a call is in
progress or whether a primary mobile station is registered, if the interference score
of the current operational frequency rises above a first low threshold (Lt) or above
the high threshold (Ht), the cordless cellular base station 10 automatically switches
its operational frequency to the first backup frequency as described in more detail
below. The cordless cellular base station 10 also removes backup frequencies from
the back-up frequency list if the interference score for that backup frequency rises
above the high threshold (Ht).
[0017] In another aspect of the present invention, the cordless cellular base station needs
to locate a specified number of frequencies having score values below the high threshold
value (Ht). If a sufficient number of frequencies are not available, the cordless
cellular base station notifies the cellular network of the problem. In one embodiment,
when the cordless cellular base station notifies the cellular network of the problem,
the cellular network will provide the cordless cellular base station with a list of
alternative authorized frequencies. In another embodiment, the cellular network will
temporarily lower the specified number of frequencies having score values below the
high threshold value (Ht) that are needed, thus enabling the cordless cellular base
station to continue to operate. In still another embodiment, if an insufficient number
of frequencies are available, the cordless cellular base station may continue to take
frequency measurements and will cease transmission until a sufficient number of clear
frequencies are available.
[0018] The cellular network initially provides the cordless cellular base station in an
authorization message a list of operational frequencies in the cellular spectrum in
which to operate. In one embodiment, the list includes all of the possible voice channels
in the cellular spectrum. In another embodiment, the list includes a small portion
of the entire cellular spectrum.
[0019] In another aspect of the present invention, the cordless cellular base station periodically
initiates a phone call to a cordless cellular base station visitor location register
(CCBS VLR). The CCBS VLR is a data base which is used to keep track of the location
of visiting mobile stations which have registered with a cordless cellular base station.
In one embodiment, the CCBS VLR contains additional storage space to receive data
regarding interference scores for the cellular frequencies which are reported by the
cordless cellular base stations. After receiving the initial call from the cordless
cellular base station, the cellular network sends a message to the cordless cellular
base station indicating that it is ready to receive the interference score data. Next,
the cordless cellular base station downloads all of the interference scores for all
of its authorized frequencies to the CCBS VLR. The CCBS VLR forwards the interference
score information to a data collection node in the cellular network. The cellular
network uses these interference scores to assist in assigning or re-assigning the
operational frequencies for the regional cells.
[0020] In another aspect of the present invention, during any contact between the cellular
network and the cordless cellular base station, such as during a location update or
a network cancellation procedure, the cellular network has the ability to update the
operational parameters in the cordless cellular base station by sending the cordless
cellular base station a new authorization message. The new authorization message may
be sent in response to any request sent to the cellular network. The update is useful
for revising the cordless cellular base station operation to accommodate for changes
in the service in the area around the cordless cellular base station and to update
the cordless cellular base station regarding changed features of the cellular network.
For example, the cellular network may temporarily alter the telephone number(s) that
the cordless cellular base station calls to access the location update/call forwarding
feature or the-cellular network may revise the allowable frequencies of the cordless
cellular base station.
[0021] In another aspect of the present invention, in order to enable the cellular network
to periodically change the operational parameters of the cordless cellular base station,
the cordless cellular base station preferably includes a preset timer which counts
down the amount of time since the cordless cellular base station last contacted the
cellular network. When the timer expires, the cordless cellular base station automatically
calls the cellular network. In the preferred embodiment, the timer is set for thirty
days, thus if the cordless cellular base station has not contacted the cellular network
within the last thirty days, for example, to request a location update for a registered
mobile station, the cordless cellular base station automatically contacts the cellular
network. In response, the cellular network determines if it is necessary to send the
cordless cellular base station a new authorization message. If a new authorization
message is required, the cellular network sends the message to the cordless cellular
base station. If a new authorization message is not required, the cellular network
sends a return result message to the cordless cellular base station. Upon receiving
either message from the cellular network, the timer in the cordless cellular base
station is reset for thirty days. This feature is useful in preventing fraudulent
usage of a cordless cellular base station. For example, if the owner did not pay his/her
bill for the service and also stopped using his or her phone away from the cordless
cellular base station, it would be difficult for the cellular network to cancel the
operation of the cordless cellular base station, because the cordless cellular base
station would never contact the cellular network. With the automatic contact feature,
the cordless cellular base station would automatically contact the cellular network
within the time specified on the preset timer. The network would, if necessary, send
a new authorization message removing all of the operating frequencies from the cordless
cellular base station which belonged to the non-paying customer, thus making the cordless
cellular base station inoperable.
[0022] In another aspect of the present invention, when a call is initiated by a mobile
station that is registered with the cordless cellular base station, the cordless cellular
base station initially checks to see if the phone number matches the MIN for one of
the other mobile stations which is listed in standby mode in the registration table
on the cordless cellular base station. If the phone number matches a MIN for the one
of the mobile stations listed in standby mode, the cordless cellular base station
pages that mobile station and initiates an intercom conversation between the two mobile
stations. The intercom feature is described in more detail below. The intercom conversation
does not utilize the landline, so the telephone extensions corrected directly to the
landline can initiate and receive calls over the landline.
[0023] In another aspect of the present invention, when a user wants to use a mobile station
which was not previously registered with the cordless cellular base station, the user
presses the initial registration button on the cordless cellular base station which
initiates an initial registration procedure. The user of the mobile station may then
depress a test registration function key on the mobile station which causes the mobile
station to send out a test registration message to the cordless cellular base station.
The test registration message is specified by the IS-136 standard. The cordless cellular
base station checks to see if the test registration message is received from a mobile
station within a specified time period, preferably thirty seconds. If a test registration
message is received, the cordless cellular base station determines if the registration
list is full. If there is no room in the registration list for an additional mobile
station, the cordless cellular base station bumps off a dormant non-primary mobile
station from the list. If there are no non-primary mobile stations which are dormant,
the cordless cellular base station sends a negative test registration response to
the mobile station and the initial registration attempt is terminated. If there is
room in the registration list for an additional mobile station, the cordless cellular
base station sends a positive test registration response message to the mobile station.
Upon receiving a positive test registration response, the mobile station will display
a set of alpha characters transmitted by the cordless cellular base station in the
positive test registration response message which are then stored by the mobile station.
In the preferred embodiment, the alpha characters which are displayed form the word
"Cordless". At this time, the mobile station may decide to attempt cordless registration
with the cordless cellular base station. If the user wishes to attempt the registration,
the mobile station sends a registration message to the cordless cellular base station.
If a registration is not desired, no message is sent to the cordless cellular base
station. Once the cordless cellular base station receives the registration message,
the cordless cellular base station completes the registration procedure and sends
a registration accept message to the mobile station. In subsequent automatic registration
attempts, once the mobile station recognizes the Residential System ID (RSID) of the
cordless cellular base station, the mobile station will display the stored alpha characters,
such as, "Cordless" to indicate that the mobile station has automatically registered
with the cordless cellular base station.
[0024] In another aspect of the present invention, the cordless cellular base station advantageously
utilizes two separate antennas - a transmit (Tx) antenna and receive (Rx) antenna
Preferably, the transmit and receive antennas are simple antennas, since the coverage
area for the cordless cellular base station is small. In a preferred embodiment, the
transmit antenna and receive antenna are physically separated on the cordless cellular
base station. Further, their signals are transmitted to the cellular transceiver along
separate paths to eliminate the need for a duplexer, thereby simplifying the design
and reducing manufacturing costs.
[0025] Advantageously, in another aspect of the present invention, a single receiver is
used by the cordless cellular base station to both receive the mobile station transmissions
and to take noise measurements which saves in the cost of the cordless cellular base
station and reduces the size of the cordless cellular base station. In order to accurately
receive the signals from the mobile station, the sensitivity of the receiver on the
cordless cellular base station can be significantly less than the sensitivity to measure
the noise in the surrounding environment. Advantageously, when the receiver is waiting
to receive a mobile station transmission, the sensitivity of the receiver is lowered
to enable it to receive higher powered transmission. When the receiver is taking an
interference measurement, the sensitivity of the receiver is increased to enable it
to receive lower power transmissions. By changing the sensitivity of the receiver
for normal reception and for interference measurements, the cordless cellular base
station can advantageously use the same receiver for both tasks.
Brief Description of the Drawings
[0026]
Figure I is a schematic block diagram of a cordless cellular system of the preferred
embodiment in communication with a cellular network and a public switched telephone
network and shown in use with a cellular network compatible mobile unit.
Figure 2 is a partial schematic block diagram of a cordless cellular system of the
preferred embodiment in communication with a plurality of cellular network compatible
mobile units and a public switched telephone network.
Figure 3 is a block diagram of the cordless cellular base station hardware of the
preferred embodiment.
Figure 4 is a schematic diagram of the TDMA time slot usage for a cordless cellular
base station receive frame and for a cordless cellular base station transmit frame.
Figure 5 is a block diagram of the mobile station hardware of the preferred embodiment.
Figure 6 is a schematic diagram of a memory storage table in the mobile station which
stores data regarding certain cordless cellular base stations with which the mobile
station communicates.
Figure 7 is a diagram illustrating the steps associated with the cordless cellular
base station initial authorization feature.
Figure 8 is a schematic diagram of the registration list which is maintained by the
cordless cellular base station.
Figure 9 is a diagram illustrating the communication between the cordless cellular
base station and the mobile station associated with an initial registration of a mobile
station.
Figure 10 is a flow chart illustrating the steps that the cordless cellular base station
takes to process an initial registration request.
Figure 11 is a flow chart illustrating the steps that the mobile station takes to
determine its location before attempting automatic registration with a cordless cellular
base station.
Figure 12 is a flow chart illustrating the automatic registration of a mobile station
to a cordless cellular base station.
Figure 13 is a flow chart illustrating the network update attempt procedure of the
cordless cellular base station.
Figure 14a is a diagram illustrating the steps associated with one embodiment of the
cordless cellular base station network update of forwarding feature.
Figure 14b is a diagram illustrating the steps associated with an alternate embodiment
of the cordless cellular base station network update of forwarding feature.
Figure 15 is a schematic block diagram of the communications between the cordless
cellular base station and the cellular network to forward calls for the mobile stations
serviced by the cordless cellular base station.
Figure 16 is a schematic block diagram illustrating one embodiment of the extension
voice combining circuitry of the cordless cellular base station.
Figure 17 is a schematic block diagram illustrating a second embodiment of the extension
voice combining circuitry of the cordless cellular base station.
Figure 18 is a schematic block diagram illustrating a third embodiment of the extension
voice combining circuitry of the cordless cellular base station.
Figure 19a is a diagram illustrating the steps associated with one embodiment of the
cordless cellular base station network cancellation of forwarding feature.
Figure 19b is a diagram illustrating the steps associated with an alternate embodiment
of the cordless cellular base station network cancellation of forwarding feature.
Figure 20 is a graph of the staircase function used to translate the noise plus interference
power level into a score increment.
Figure 21 is a graph of the variations in an exemplary interference score over time.
Figure 22 is a drawing of an exemplary score of a variety of frequencies over time.
Detailed Description of the Preferred Embodiments
General Description of System Operation
[0027] The preferred embodiment of the wireless communication system of the present invention,
as illustrated in Figures 1 and 2, comprises a cordless cellular base station 10.
The cordless cellular base station is capable of communicating with a cellular network
compatible mobile station 12. The cordless cellular base station 10, algor referred
to as a limited or selective access base station, is connected to a landline 14 on
a public switched telephone network (PSTN) 15 and is assigned a landline identification
number (LLN) or telephone number. Further, the cordless cellular base station 10 is
assigned an electronic serial number at the time of manufacture for identification
purposes. The electronic serial number is generally stored in permanent memory in
the cordless cellular base station so the serial number cannot be tampered with by
unauthorized personnel. The mobile station 12 is registered with a cellular network
16 and is assigned a mobile station identification number (MIN) which is the telephone
number of the mobile station. Further, the mobile station, at the time of manufacture,
is assigned an electronic serial number (ESN). The ESN is generally stored in the
permanent memory, in the mobile station. As is known to those of skill in the art,
the cellular network 16 is connected to the public switched telephone network to route
calls to/from callers on the cellular network 16 from/to callers on the public switched
telephone network (PSTN) 15.
[0028] The mobile stations 12 are capable of communicating with both cellular base stations
18 on the cellular network 16 and with cordless cellular base stations 10. When a
mobile station 12 is communicating with the cellular network 16, it is referred to
as being in regional cellular service mode. When a mobile station 12 is communicating
with the cordless cellular base station 10, it is referred to as being in cordless
telephone landline service mode.
[0029] When a mobile station 12 comes within range of a cordless cellular base station 10
with which it has previously registered, as described in more detail below and in
accordance with the preferred embodiment, the mobile station 12 automatically switches
from the regional cellular service mode to the cordless telephone landline service
mode without user intervention. Once the mobile station 12 has confirmed with the
cordless cellular base station 10 that the mobile station 12 has switched to cordless
landline service mode, the cordless cellular base station 10 communicates with the
cellular network 16 to provide a call forwarding update message. The call forwarding
update message requests that the cellular network 16 route all calls for the mobile
station 12 to the landline number associated with the cordless cellular base station
10. In addition, while the mobile station 12 remains within range of the cordless
cellular base station 10, all calls placed on the mobile station 12 are sent through
the cordless cellular base station 10 to the associated landline 14 and out onto the
PSTN 15. Preferably, there is no handoff of telephone calls between the regional cellular
network 16 and cordless cellular base station 10 environments. For example, if a call
is initiated via the cordless cellular base station 10 and the mobile station 12 moves
to an area outside of the range of the cordless cellular base station's cell 17, the
call is disconnected instead of being transferred to the cellular network 16. In an
alternate embodiment, handoff of telephone calls between the regional cellular network
16 and cordless cellular base station 10 environments is enabled. For example, if
a call is initiated via the cordless cellular base station 10 and the mobile station
12 moves to an area outside of the range of the cordless cellular base station's cell
17, the call is automatically switched through the cordless cellular base station
10 and its associated landline 14 to the cellular network 16. The cellular network
16 then routes the call through the cellular base station 10 to the user's mobile
station 12 in a manner similar to the handoff procedure between adjacent cells in
a conventional cellular system.
[0030] Typically, when the mobile station 12 severs contact with the cordless cellular base
station 10, the cordless cellular base station 10 sends a network forwarding cancellation
message to the cellular network 16 to cancel the forwarding of calls for the mobile
station identification number to the landline number associated with the cordless
cellular base station 10. The cordless cellular base station 10 is informed during
the initial authorization message which types of registration/deregistration activities
for which the network 16 wants to be informed. Some examples of types of deregistration
events for which the network 16 may want to be contacted are: when the mobile station
12 is turned off, i.e., a power down deregistration or due to a manual cancellation
of the cordless service mode, i.e., forced deregistration. When the mobile station
12 severs contact with the cordless cellular base station 10 for reasons other than
powering off, the mobile station 12 may register with the local regional cellular
base station of the regional cellular network 16. Once the mobile station 12 is registered
with the regional cell, calls to the users mobile identification number are directly
routed by the cellular network 16 to the mobile station 12.
Cordless Cellular Base Station
Cordless Cellular Base Station (CCBS) Hardware
[0031] The cordless cellular base station 10 communicates over the land line 14 and with
the mobile station 12 using a digital cellular transceiver. The cordless cellular
base station uses time division multiple access (TDMA) communication to communicate
with the mobile station 12.
[0032] In a preferred embodiment, the hardware of the cordless cellular base station 10
is very similar to the hardware used for a mobile station, however the functionality
of the cordless cellular base station 16 is similar to a base station for a regional
cell. The most significant differences between the cordless cellular base station
and a typical base station are that the cordless cellular base station preferably
has only one transceiver (permitting the use of only one set of transmit and receive
frequency channel at one time) and that it supports only digital traffic. These differences
permit the cordless cellular base station to be configured in a reasonable size for
home use. As illustrated in Figure 3, the CCBS comprises a microprocessor or a microcontroller
20, an associated memory storage area 21, a baseband modem 22, a cellular transceiver
23, a transmit (Tx) antenna 24, a receive (Rx) antenna 25, user interface hardware
26, a modem 27, a switch 28 and standard telephone interface hardware 29. The processor
20 is in communication with the memory 21, the user interface 26, the modem 27, the
baseband modem 22, and the cellular transceiver 23 in a well known way. The processor
20 controls the operation of the radio portion of the cordless cellular base station
hardware, i.e., the operation of the baseband modem 22 and cellular transceiver 23.
The processor 20 also controls the operation of the call processing tasks and the
administrative tasks related to communication with the cellular network 16. Finally,
the processor 20 controls the user interface 26. Preferably, the digital cellular
transceiver 23 and processor 20 together communicate with the mobile station utilizing
the IS-136 standard air interface communications protocol. The associated memory storage
area 21 comprises both permanent and temporary memory storage capabilities.
[0033] The baseband modem 22 is preferably implemented using a digital signal processor
(DSP). Preferably, the baseband modem 22 used in the cordless cellular base station
10 provides the same type of function as is used in local cellular base stations 18.
The baseband modem 22 is used to implement the time division multiple access (TDMA)
protocol in accordance with the IS-136 standard. Further, the baseband modem 22 performs
the coding of the voice signals which digitally compresses and encodes the analog
voice messages to/from the landline from/to the mobile station for faster transmission
across the cellular channel, as known to those of skill in the art. In the preferred
embodiment, VSELP coding is used; however, other compressing and coding schemes known
to those of skill in the art, such as the International Telecommunications Union (ITU)
compression and coding schemes, may be utilized. Finally, the baseband modem 22 performs
the signal processing functions associated with voice detection to differentiate between
noise and voice signals and echo cancellation to alleviate echoes picked up by the
microphone in the mobile stations 12 which are common signal processing functions
performed by base stations.
[0034] The cellular transceiver 23 comprises a transmitter (Tx) 30 and a receiver (Rx) 31.
In a preferred embodiment, the cellular transceiver 23 is a digital transceiver. In
a more preferred embodiment, the digital cellular transceiver 23 is a time division
multiple access (TDMA) transceiver. Preferably, the transmitter 30 is the similar
to the transmitter that is used in the mobile station 12. Preferably, the functionality
of the transmitter is compliant with the IS-138 minimum performance requirements for
a digital base station standard except for the exceptions listed below. The IS-138
standard is well known to those of skill in the art and is hereby incorporated by
reference in its entirety. The IS-138 standard can be obtained through the Telecommunications
Industry Association (TIA), Engineering Department, 2001 Pennsylvania Avenue, N.W.,
Washington, D.C. 20006. The first exception is that the transmitter of the cordless
cellular base station emits much less power than a standard cellular base station,
since the output power of the cordless cellular base station 10 is designed to communicate
only with mobile stations 12 in a small surrounding area. Preferably, the transmitter
30 transmits at an output power of 6.3 mW. In another embodiment, the transmitter
30 transmits at an output power of approximately 10 mW. Additional exceptions for
the transceiver to the IS-138 standard are that the frequency tolerance of the cordless
cellular base station is 1.0 parts per million (ppm) and that time slot 4 is usually
silent except for the transmission of the synch word as described in more detail below.
The receiver 31 is similar to the receivers that are used in a standard cellular telephone,
in that the receiver 31 of the cordless cellular base station 10 is able to receive
at a fairly high sensitivity in the mobile receive band in order to be able to search
for other nearby base station signals. Advantageously, a single receiver is used to
both receive the mobile station transmissions and to take noise measurements which
saves in the cost of the cordless cellular base station and reduces the size of the
cordless cellular base station. In the preferred embodiment, the dynamic range of
the receiver is approximately 70 dB, that is, the receiver can receive signals which
are within a 70 dB range. In order to accurately receive the signals from the mobile
station 12, the sensitivity of the receiver 31 on the cordless cellular base station
10 must be significantly less than the sensitivity to measure the noise in the surrounding
environment. This is because the mobile station is expected to be used very close
to the base station. Thus, when the receiver 31 is waiting to receive a mobile station
transmission, the sensitivity of the receiver is less to enable it to receive higher
powered transmissions. In the preferred embodiment, the 70 dB dynamic range of the
receiver is scaled to receive transmissions from the mobile station 12 in the -20
dBm to -90 dBm range. When the receiver 31 is waiting to take an interference measurement,
the sensitivity of the receiver 31 is increased to enable it to receive lower power
transmissions. In the preferred embodiment, the 70 dB dynamic range of the receiver
31 is scaled to receive transmissions in the -46 dBm to -116 dBm range. In an alternate
embodiment, the CCBS uses a non-linear front end receiver to provide increased dynamic
range. As will be recognized by those of skill in the art, the fact that the CCBS
does not require an equalizer enables the non-linear front end receiver to be easily
substituted for the preferred receiver described above.
[0035] By utilizing only a digital transceiver 23 to communicate with the mobile station
12, the hardware and software of the cordless cellular base station 10 is less complicated
and therefore, the cost to manufacture the cordless cellular base station 10 is reduced.
The IS-136 standard calls for base station and mobile stations that operate in TDMA
digital mode on the digital channels and in an analog mode on analog channels. While
it is preferred to provide cordless cellular base station that operates only in a
digital mode on the digital channels, it is contemplated that a cordless cellular
base station could be provided such that it operates in both analog and digital modes.
[0036] The transmit (Tx) antenna 24 and receive (Rx) antenna 25 are simple antennas, since
the coverage area for the cordless cellular base station 10 is small. In a preferred
embodiment, the transmit antenna 24 and receive antenna 25 are separate antennas which
are physically separated on the cordless cellular base station 10. Further, their
signals are transmitted to the transceiver 23 along separate paths to eliminate the
need for a duplexer, thereby simplifying the design and reducing manufacturing costs.
However, it is contemplated that in some cases a common antenna for both transmission
and receive functions may be advantageous and in the common antenna embodiment a duplexer
is added to the cordless cellular base station hardware. Duplexers are well known
devices that permit signals of different frequencies to be sent and received at the
same time over the same antenna. In one embodiment, the transmit and receive antennas
are internal antennas that do not extend outside of the cordless cellular base station.
[0037] The user interface hardware 26 is capable of providing an interface between a keypad
32 and a display 33. In a preferred embodiment, the keypad 32 includes the standard
telephone twelve-key keypad. In other embodiments, the keypad 32 may include additional
function keys. The display 33 is preferably an LCD display capable of displaying a
variety of types of information to the user. The display 33 in a simpler embodiment
may include a plurality of seven-segment displays or one or more simple LEDs. The
standard telephone interface hardware 29 is utilized to communicate with the landline
14 and the PSTN 15 utilizing control signals and a communications protocol which are
commonly known in the art. Preferably, the standard telephone interface hardware 29
includes a standard four-wire-to-two wire hybrid device to convert the signals on
four wires from the cordless cellular base station hardware to the two wire standard
of landline communication. In addition, the telephone interface hardware 29 provides
ring detection and the-closing of a subscriber loop under command of the controller
20. In a preferred embodiment, the cordless cellular base station 10 appears to the
PSTN 15 as if it were a standard 2500 series telephone. Thus, for example, the base
station 10 advantageously supports both pulse and DTMF dialing. The cordless cellular
base station 10 also includes a standard data modem 27 for use in transmitting data
over an ordinary telephone line. This permits a modem link to be set up between the
cordless cellular base station 10 and another system using its associated landline
14.
[0038] Finally, the cordless cellular base station hardware includes a power supply 34.
The power supply 34 comprises the circuits to define and regulate voltages supplied
to the above-referenced hardware elements of the cordless cellular base station 10.
At least one connection is made to obtain power from a main source, such as a wall
socket in a home. The power supply 34 may also include an alternate connection to
which a battery may be connected and charged.
Cordless Cellular Base Station Operation
[0039] Referring back to Figures 1 and 2, the cordless cellular base station 10 supports
the following functions, which are described in more detail hereafter. A network authorization
procedure initializes the communication between the cordless cellular base station
10 and the cellular network 16. After the network authorization procedure is complete,
the cordless cellular base station 10 enables registration of mobile stations 12 for
use with the cordless cellular base station 10. Registration of a mobile station 12
with the cordless cellular base station 10, as described in more detail below, enables
the mobile station 12 to receive calls addressed to its mobile station identification
number at the landline number associated with the cordless cellular base station 10.
The cordless cellular base station 10 maintains a list of the mobile stations 12 most
recently granted registration privileges with the cordless cellular base station 10.
[0040] In the preferred embodiment, while the mobile station 12 is listed on the registration
list of a particular cordless cellular base station 10, the mobile station 12 automatically
registers with the cordless cellular base station 10 when the mobile station 12 comes
into-proximity with the cordless cellular base station 10. This automatic registration
of the mobile station 12 with the cordless cellular base station 10 occurs because
the mobile station 12 stores information about the regional cellular network service
16 in the vicinity of the cordless cellular base station as described in more detail
below. When the mobile station 12 recognizes that it is located in the portion of
the regional cellular network 16 which is near the cordless cellular base station
10 that it has recently registered with, the mobile station begins to search for the
cordless cellular base station 10. The cordless cellular base station 10 is always
transmitting a digital control channel signal (DCCH), which is well known to those
of skill in the art, for the mobile station 12 to locate. Once the mobile station
12 finds the cordless cellular base station 10, an automatic registration procedure,
which is described in more detail below, is invoked which enables the mobile station
12 to receive calls directed to its mobile station identification number at the landline
number associated with the cordless cellular base station 10.
[0041] The cordless cellular base station 10 is advantageously able to support the registration
of up to ten mobile stations 12 at a given time, i.e., up to ten mobile stations 12
may be communicating with the cordless cellular base station 10 to have the regional
cellular network 16 forward calls for their respective mobile stations 12 to the landline
number associated with the cordless cellular base station 10. If a mobile station
12 is registered with the cordless cellular base station 10 and is not on a call,
the mobile station 12 is considered to be in a "standby" state, that is, it is standing
by ready to transmit or receive a call. When a call is received on the landline associated
with the cordless cellular base station 10, the cordless cellular base station 10
pages all of the registered mobile stations 12, using the paging processes known to
those of skill in the art, which is the same as a cellular base station 18 paging
a mobile station 12, and all of the mobile stations 12 will "ring" indicating an incoming
call. To answer the incoming call, any one of the mobile station users depresses the
send key on the mobile station handset 12 and will be connected through the cordless
cellular base station 10 to accept the call. When the mobile station 12 accepts a
call by pressing the send key or transmits a call, the mobile station 12 is considered
to be in an "active" state, that is, it is actively processing a call. The cordless
cellular base station of the preferred embodiment can support two "active" mobile
stations, that is, up to two mobile stations can communicate with each other or with
a caller on the landline through the cordless cellular base station 10. Thus, in the
preferred embodiment, the first two mobile stations to answer a call will be connected
to the call. The remaining mobile stations are locked out and any attempt by any of
the mobile stations to answer the call will result in an error indication by the phone
to the user. In order to accept more "active" mobile stations 12, additional transceivers,
call processing hardware and software can be added to the cordless cellular base station
10, as known to those of skill in the art.
[0042] The cordless cellular base station 10 can support two mobile stations 12 because
of the manner that the cordless cellular base station 10 uses the time slots of a
single TDMA frame to transmit and receive information. In accordance with the IS-136
standard, the TDMA signal has six time slots, referred to as time slot 1 to time slot
6 (37-42) respectively, and as illustrated in Figure 4. In a cordless cellular base
station receive time frame 35, the following information is received by the mobile
station 12 in each of the time slots (37-42), respectively. In'time slot 1 (37) the
cordless cellular base station 10 receives the digital control channel (DCCH) messages,
in accordance with the IS-136 standard, from the mobile station 12 in the same manner
that a digital cellular base station in a regional cell 18 receives DCCH messages
from a mobile station 12. For example, the DCCH messages contain the information that
the mobile station 12 must exchange with the cordless cellular base station 10 to
maintain registration with the cordless cellular base station 12. In time slot 2 (38)
and time slot 5 (41), the cordless cellular base station 10 receives voice data from
a second mobile station (MS2). In time slot 3 (39) and time slot 6 (42), the cordless
cellular base station 10 receives voice data from a first mobile station (MS1). In
time slot 4 (40), no data is received from the mobile station 12 in the cordless cellular
base station 10 which is shown as an open time slot.
[0043] In a cordless cellular base station transmission time frame 36, the following information
is transmitted by the cordless cellular base station 10 in each time slot, 3742, respectively.
In time slot 1 (37), the cordless cellular base station 10 transmits digital control
channel (DCCH) messages, in accordance with the IS-136 standard, in the same manner
that a digital cellular base station in a regional cellular network transmits DCCH
information. For example, the DCCH messages contain the information that the mobile
station 12 looks for to register with the cordless cellular base station 10 when it
recognizes that it is in proximity to it. In time slot 2 (38) and time slot 5 (41),
the cordless cellular base station 10 transmits voice data to a second mobile station
(MS2). In time slot 3 (39) and time slot 6 (42), the cordless cellular base station
10 transmits voice data to a first mobile station (MS1). Since the digital control
channel (DCCH) is preferably a half-rate digital control channel, the DCCH does not
have to be transmitted in time slot 4 (40). Therefore, time slot 4 usually only transmits
the synch word which helps mobile stations synchronize their transmission with the
cordless cellular base station. However, to prevent the cordless cellular base station
10 from accidentally not being detected by another cordless cellular base station
10 should their transmission be in sync the cordless cellular base station 10 randomly
transmits an idle code in addition to the synch word on time slot four. By occasionally
transmitting an idle code at random time intervals on time slot 4, the probability
that the CCBS will be detected by any of the cordless cellular base stations which
are transmitting in sync is increased. For the remainder of the time, timeslot 4 (40)
is silent besides the transmission of the synch word to gather noise information regarding
the environment in which the cordless cellular base station 10 resides. Thus, at randomly
selected frames, the cordless cellular base station 10 transmits an idle code in Time
Slot 4 (40) instead of being silent to notify nearby cordless cellular base stations
10 of its existence during this time slot 40. The average rate of these transmissions
is preferably between one in two hundred fifty-six and one in eight TDMA frames. Preferably,
the frames in which the idle code is transmitted are selected by either a non-deterministic
process or by a pseudo-random decision process that yields different selection patterns
for different cordless cellular base stations 10.
[0044] When the mobile station 12 moves out of the range of the cordless cellular base station
10, the cordless cellular base station 10 automatically sends a message to the regional
cellular network 16 to cancel the call forwarding of phone calls addressed to the
mobile station identification number of the mobile station 12, as described in more
detail below. In the preferred embodiment, if the mobile station 12 is on a call,
the call is dropped and the mobile station 12 will have to reinitiate the call through
the regional cellular network 16. In an alternate embodiment, the call is maintained
by automatically forwarding the call to the mobile station 12 through the regional
cellular network 16. In either case, after the mobile station 12 is no longer in the
range of the cordless cellular network 16, the mobile station 12 automatically registers
with the regional cellular network 16 to accept calls in the traditional cellular
service manner.
Mobile Station
Mobile Station Hardware
[0045] In a preferred embodiment, the hardware of the mobile station 12, as illustrated
in Figure 5, comprises a processor 46, an associated memory storage area 47, a digital
cellular transceiver 50, an analog cellular transceiver 52, user interface hardware
44, and handset I/O control logic 45. Advantageously, the digital cellular transceiver
50 and the analog cellular transceiver 52 are actually incorporated into the same
cellular transceiver device as in the cordless cellular base station, however, for
simplicity of understanding are shown as two separate devices in Figure 5. The processor
46 is in communication with each of the above indicated elements. The associated memory
storage area 47 comprises both permanent and temporary memory storage capabilities.
The digital cellular transceiver 50 comprises a receiver (Rx) 48 and a transmitter
(Tx) 49. In a preferred embodiment, the digital cellular transceiver 50 is a time
division multiple access (TDMA) transceiver. The analog cellular transceiver 52 comprises
a receiver (Rx) 53 and a transmitter (Tx) 54. The user interface hardware 50 is capable
of providing an interface between a keypad 55 and a display 56. In a preferred embodiment,
the keypad 55 includes at least the standard telephone twelve-key keypad. In other
embodiments, the keypad 55 may include additional function keys. The display 56 is
preferably an LCD display capable of displaying a variety of types of information
to the user. The display 56, in a simpler embodiment, may include a plurality of seven-segment
displays. The handset I/O control logic 45 provides an interface between a standard
telephone microphone pickup 60 and speaker 59 on a conventional handset of a mobile
station 12 as is commonly known to those in the art. Preferably, the mobile station
12 meets all of the requirements of the IS-137 performance requirements for a mobile
station standard, which is hereby incorporated by reference in its entirety. The IS-137
standard can be obtained through the Telecommunications Industry Association (TIA),
Engineering Department, 2001 Pennsylvania Avenue, N.W., Washington, D.C. 20006.
Mobile Station Operation
[0046] Referring back to Figures 1-2, the mobile station 12 preferably comprises a dual-mode
cellular handset that is capable of accessing either digital or analog channels in
a regional cell 18 of the cellular network 16. The mobile station 12 communicates
with the cellular network 16, i.e., with the local cells 18, and with the cordless
cellular base station 10 utilizing the same cellular frequency ranges and utilizing
a single communications protocol. In a preferred embodiment, the mobile station 12
utilizes the IS-136 air interface standard, to communicate with both the cellular
network 16 and the cordless cellular base station 10. The IS-136 standard forms a
compatibility standard for time division multiple access (TDMA) digital cellular mobile
telecommunication systems to ensure that a mobile station 12 can obtain service in
any cellular system manufactured in accordance with the standard. In the preferred
embodiment, the cordless cellular base station 10 uses only the TDMA digital protocol
from the IS-136 standard and thus, the mobile station 12 only utilizes its digital
transceiver 50 (Figure 5) to communicate with the cordless cellular base station 10.
However, in other embodiments the mobile station may also be compliant with other
communications standards such as such as those standards which are compliant with
1.9 GHz operation, such as provisional standard PN-3388 which is also available from
the Telecommunications Industry Association (TIA).
[0047] Preferably, the mobile station 12 has an initial preference for its last network
registration; that is, when the mobile station 12 is powered ON, the mobile station
12 automatically synchronizes to is last operating frequency and attempts to register
with the control channel on that frequency. If it fails to locate a control channel
on that frequency, the mobile station will scan the other frequencies to locate the
best control channel. Most likely, the mobile station will end up registering with
the closest regional cellular base station 18 in the cellular network 16. After it
has registered with the regional cellular network, as described in more detail below,
when the mobile station 12 comes into proximity with a cordless cellular base station
10 with which it has been granted automatic registration privileges, the mobile station
12 automatically deregisters from the regional cellular network 16 and registers with
the cordless cellular base station 10. As described briefly above and in more detail
below, the mobile station 12 stores information regarding the cellular service in
the area surrounding the cordless cellular base stations 10 with which it has recently
registered. Thus, the mobile station 12 constantly compares the information about
the regional cell 18 it is currently in to see if it is a cell that is likely to contain
one of the cordless cellular base stations 10 with which it has most recently registered.
If it is in a regional cell 18 that is likely to contain a cordless cellular base
station 10 that it has recently registered with, it attempts to locate that cordless
cellular base station 10 utilizing information that it has stored about the operating
parameters of the cordless cellular base station 10.
[0048] Therefore, the mobile station 12 includes a certain portion of its memory 47 (Figure
5) that is dedicated to the semi-permanent storage of the operating frequency and
other information related to one or more cordless cellular base stations 10 with which
it has recently registered. Preferably, the mobile station 12 semi-permanently retains,
in an EEPROM, a cordless cellular base station storage table 78, as illustrated in
Figure 6, which stores information about three cordless cellular base stations with
which it has previously registered. While storage for three cordless cellular base
stations 10 is currently preferred, it is contemplated that appropriate applications
storage for additional cordless cellular base stations 10 is possible. A top row 80
holds data for a "primary" cordless cellular base station. The "primary" cordless
cellular base station is, for example, the cordless cellular base station 10 in the
user's home or office, which is most often accessed by the user and is responsible
for the bills associated with the subscription to this service. The user defines which
cordless cellular base station is the "primary" base station. In a preferred embodiment,
after the mobile station 12 initially registers with the cordless cellular base station
10, the user enters a specified keystroke procedure, which may advantageously be entering
the number 1 key followed by the # key on the mobile station keypad, to allow the
user to designate the cordless cellular base station 10 currently in use as the "primary"
cordless cellular base station. The second and third rows 82, 84 advantageously hold
data for the two most recently used non-primary cordless cellular base stations 10
in the order of most recent use. The mobile station 12 maintains the information for
the primary cordless cellular base station at all times in the top row 80. The mobile
station 12 manages the ordering of the lower rows, shuffling them as necessary to
ensure that the second row 82 has the data for the non-primary cordless cellular base
station 10 used most recently, and the third row 84 has the data for the non-primary
cordless cellular base station 10 used next most recently.
[0049] In the horizontal direction, the table 78 is divided into first and second parts
85, 87. The first part 85 of the table 78 stores information about the cordless cellular
base station 10, such as the cordless cellular base station identification number
and last known operating channel and back-up channel for the cordless cellular base
stations 10. The second part 87 of the table 78 stores information about the cellular
service for the regional cell 18 in which the cordless cellular base station 10 exists.
[0050] The first part 85 of the table 78 preferably includes the following information regarding
the cordless cellular base station 10: a Residential System ID (RSID) 86, the operating
channel f
o 88, and back up channels f
1, f
2, and f
3 90-94 respectively, the country code CC 96 and the system operating code SOC 98.
The RSID is a 16-bit serial number that identifies the cordless cellular base station
10. The RSID is assigned to the cordless cellular base station by the cellular network
16 during its initial authorization procedure. The RSID 86 is broadcast by the cordless
cellular base station 10 over the digital control channel (DCCH) in accordance with
the IS-136 standard for the mobile station 12 to recogmze and to attempt to register
with the cordless cellular base station 10. The mobile station 12 restores the RSID
in the table 78 after the initial registration with the cordless cellular base station
10 to help the mobile station 12 relocate the cordless cellular base station 10 the
next time it comes within range. The channel information is the current or last known
operating channel f
0 88, and three alternative channels f
1, f
2, and f
3 90-94, respectively, on which the cordless cellular base station 10 may operate.
The alternate channels are the channels on which the digital control channel (DCCH)
for the cordless cellular base station would most likely be detected. These channels
are determined by the cordless cellular base station 10 based on its measurement of
the interference environment using a procedure which is described in more detail below.
Preferably, the cordless cellular base station 10 broadcasts a neighbor list which
includes the alternate channels for cordless cellular base station operation. The
neighbor list is then stored by the mobile station. In an alternate embodiment, the
alternate channels are supplied to the mobile station 12 by the cordless cellular
base station 10 via data or other delivery packets which are periodically transmitted
by the cordless cellular base station 10 over the digital control channel (DCCH),
while the mobile station 12 is registered with the cordless cellular base station
10. The country code CC 96 is the country code for the landline 14 to which the cordless
cellular base station 10 is connected. The System Operator Code SOC 98 is the system
operator code for the service provider. In the case of a cellular network, the McCaw
network has its individual code, as do other service providers.
[0051] Together, the country code CC 96, the System Operator Code SOC 98, and the RSID 86,
are referred to herein as the "extended RSID" 100. Preferably, when the mobile station
12 is trying to determine if it has located a cordless cellular base station 10 with
which it has previously registered it compares the "extended RSID" 100 it has stored
with the broadcast extended RSID from the cordless cellular base station 10. In the
preferred embodiment, when the mobile station 12 compares a stored extended RSID 100
against a cordless cellular base station's broadcasted extended RSID for a match,
the following rules are used. If the CC 96 of the cordless cellular base station 10
was not previously obtained by the mobile station 12, the mobile station 12 treats
this as if the two CCs are known and match. In effect, an unknown CC 96 is treated
as a wild card.
[0052] Using the extended RSID 100 rather than the RSID 86 by itself provides an additional
level of protection against inadvertent registration with a cordless cellular base
station 10 in the wrong area which happen to have the same RSID as the mobile station
12 has stored. For example, you do not want your mobile station 12 to try to register
with a cordless cellular base station 10 of a person in Canada which may have the
same RSID 86 as a cordless cellular base station 10 in the United States. By using
the extended RSID 100 thus checking the country code CC 96, the system operating code
SOC 98 and the RSID 100, such errors are obviated.
[0053] The second part 87 of the table 78 includes the following information regarding the
regional cell 18 in which the cordless cellular base station 10 exists: a system identifier
SID 102 of the cell, a plurality of public service profiles PSPO, PSP" PSP2, and PSP3
104-110 which further characterize the cell 18. The System Identifier SID 102 is an
identification number for a metropolitan area within the cellular network 16 within
which the cordless cellular base station 10 is located. Each metropolitan area in
the regional cellular network 16 is assigned its own SID 102. The mobile station 12
uses the SID to identify when the mobile station 12 is in an area which is most likely
to contain a known cordless cellular base station 10. There may be several cells 18
which operate within the metropolitan area. Thus, it is advantageous to use some further
available information to help uniquely identify the cells within which a desired cordless
cellular base station is located. The Public Service Profile preferably contains,
in the case of a digital regional cell, the digital control channel (DCCH) channel
number for the regional cell and the 8-bit Digital Verification Color Code (DVCC)
number for the regional cell in which the cordless cellular base station was last
located. The DVCC is sent by the base station to the mobile station and is coded to
form the Coded Digital Verification Color Code (CDVCC). The DVCC is a 12-bit data
field which contains the 8-bit DVCC and 4 protection bits generated by the base station.
The CDVCC is sent in each time slot to and from the mobile stations and base station.
The CDVCC is used to indicate that the correct data to/from the base station from/to
the mobile station is being decoded. These numbers are well known to those in the
art. In the case of an analog regional cell, the Public Service Profile preferably
contains the Analog Control Channel number (ACCH) for the regional cell and the Digital
Color Code (DCC) number for the regional cell within which the cordless cellular base
station 10 was last located. The DCC is a digital signal transmitted by a base station
on a forward analog control channel that is used to detect capture of the appropriate
base station by a particular mobile station. These numbers are well known to those
of skill in the art. The purpose for storing the Public Service Profile is to have
additional information about the regional cellular service in which the desired cordless
cellular base station 10 is located, so that it is more likely the correct regional
cells will be identified corresponding to the cordless cellular base station.
[0054] The mobile station 12 is responsible for populating the PSP columns 104-110 of the
table 78. In order to be able to do this, in a preferred embodiment, the mobile station
12 receives the broadcast neighbor list from the cordless cellular base station 10
and infers the PSPs from the neighbor list. The neighbor list message which is typically
broadcast by a base station is specified by the IS-136 standard and includes the ability
to designate certain channels as preferred channels, certain channels as nonpreferred
channels and certain channels as regular channels. A channel designated as a preferred
channel would cause the receiving mobile station to switch its operating channel over
to this preferred channel. The non-preferred and regular channels do not require such
immediate action from the mobile station. The cordless cellular base station takes
advantage of this predefined IS-136 broadcast neighbor list message, but instead of
sending information regarding the make up of nearby peer cells over the neighbor list
message, the cordless cellular base station sends PSP information regarding the cells
which overlap the CCBS coverage area and information regarding the backup channels
that the CCBS may choose to switch to. In addition, the cordless cellular base station
may include additional channels which are not backup channels but are channels that
the CCBS wants the mobile station to be aware of. Up to four PSPs are sent over the
broadcast neighbor list and are designated as non-preferred channels. The remainder
of the neighbor list is made up of the backup channels and other channels which are
all indicated as regular channels. When the mobile station 12 receives the neighbor
list from the cordless cellular base station 10, it extracts the PSP information for
those channels which are indicated as non-preferred channels and stores this information
in the cordless cellular base station storage table 78.
[0055] The CCBS determines the channels which are to be included in the neighbor list message
as the non-preferred channels by determining the public cells that the CCBS is within
or nearby by using the following procedure. The CCBS scans all of the channels in
the cellular spectrum and performing received signal strength (RSS) measurements on
each channel. It will look at the activity on the channel having the highest RSS measurements
to see if the activity on the channel is due to a public digital control channel.
If the signal is not due to a public digital control channel, the CCBS will switch
move to the channel with the next highest RSS measurement, etc. until a 20 dB threshold
is reached. If the signal is due to a public digital control channel, the CCBS will
store this channel as an active digital control channel for a public cell whose coverage
area includes or is near that CCBS is within or nearby. The CCBS will collect the
PSP information for up to four active digital control channels for public cells that
the CCBS is within or nearby and will send this information in the broadcast neighbor
list message.
[0056] In an alternate embodiment, the mobile station 12 collects the Public Service Profile
for the regional cell 18 whenever the mobile station enters a new cell 18. During
registration with the cordless cellular base station 10, the mobile station 12 compares
the current and previous collected public service profiles (PSPs) with the previously
stored public service profiles and updates the table 78 if one or both of these public
service profiles is not already present in table 78. The reason that the public service
profile may change is that it is possible that a cordless cellular base station 10
may be located in a place over which the regional cell which provides service may
change, i.e., the cordless cellular base station may be at a location where the service
range of up to four adjacent cells overlap. By storing up to four public service profiles,
no matter which cell is servicing the mobile station 12 as it approaches the cordless
cellular base station 10, the mobile station 12 will still recognize that it needs
to try to locate the cordless cellular base station 10. The most recently collected
public service profile is always stored as PSP
0. When the public service profile changes, the public service profile that was previously
stored as PSP
0 is stored as PSP
1, and the public service profile which was stored as PSP
1 is stored as PSP
2, etc.
[0057] The term "extended Public Service Profile" 112 is used herein to mean the combination
of the SID 102 and a PSP. The mobile station 12 verifies that the current SID matches
the SID of the regional cell 18 containing the cordless cellular base station 10 before
checking the PSP. Once a SID match is found the PSPs are checked in order for a match.
The extended PSP 112 must match before the mobile station 12 begins looking for a
specific cordless cellular base station 10. For example, the mobile station 12 checks
the SID of the cell that it is presently in and compares it to SIDs for each of the
cordless cellular base stations 10 that the mobile station 12 is registered with to
determine if the mobile station 12 is in a SID that is likely to have a known cordless
cellular base station 10. In this way, the mobile station 12 does not look for a specific
cordless cellular base station 10 when the mobile station 12 is roaming in some distant
city with an unfamiliar SID. Further, the use of the SID reduces the chance that the
mobile station 12 will erroneously attempt to register with a cordless cellular base
station 10 when the mobile station 12 user is in another city or state. To further
reduce this risk, in a preferred embodiment, the extended PSP also contains the country
code, CC, for the country in which the cordless cellular base station resides which
prevents the mobile station from searching for the cordless cellular base station
when the SID matches but the mobile station is in the wrong country.
Features of the Cordless Cellular Base Station
Initial Authorization of the Cordless Cellular Base Station
[0058] In order to maintain a secure system, the cordless cellular base station 10 first
initially registers with the cellular network 16 in order to authorize its use. In
fact, the cordless cellular base station 10 is not operational without the network
authorization, as the cellular network 16 provides the cordless cellular base station
10 with certain operational parameters, such as the authorized operating frequency
list for its operation.
[0059] Preferably, when a customer purchases a cordless cellular base station 10, the seller
will contact the cellular network 16 and provide it with certain information about
the cordless cellular base station 10, such as the electronic serial number of the
cordless cellular base station 10, the landline number to which the user plans to
hookup the cordless cellular base station 10, etc. In addition, it is expected that
the seller will also provide the mobile identification number (MIN) of the primary
user's mobile station 12 to the cellular network for subscription to the call forwarding
feature.
[0060] Once the cordless cellular base station 10 is brought to the location where the cordless
cellular base station 10 will reside, the user connects the cordless cellular base
station 10 to a telephone jack 58 associated with the user's landline 14 and a power
source (not shown), such as a typical wall socket. In a preferred embodiment, the
user depresses a network authorization function key 62 on the cordless cellular base
station 10. In one alternate embodiment, once the power source is connected to the
cordless cellular base station 10, the cordless cellular base station 10 automatically
initializes a cellular network authorization procedure. Alternatively, the system
could advantageously accept a series of specified numbers and symbols on the telephone
keypad (Figure 3), such as 4648#, as instructions to manually initialize the network
authorization procedure.
[0061] As illustrated in Figure 7, the network authorization procedure for a new cordless
cellular base station 10 is described. After the automatic network authorization procedure
has been initialized or the manual keystroke commands have been depressed, the processor
46 uses the standard telephone interface hardware 29 on the cordless cellular base
station (CCBS) 10 to initiate a call to a preset cellular network authorization phone
number, such as a remote network update number, via the landline 14 in a step 64.
Preferably, the cellular network authorization number is stored in semi-permanent
memory in the cordless cellular base station 10.
[0062] After the cellular network (CN) 16 answers the call from the cordless cellular base
station 10, the cellular network 16 initiates a modem link in modem setup step 66
with the cordless cellular base station 10 on the landline 14. This modem link can
be established using the AT&T 800 Transaction Access Service Option or may be provided
by a separate modem pool. The cordless cellular base station 10 makes at least two
attempts to set up a modem link with the network 16. The modem 27 of the cordless
cellular base station 10 and a modem 27 in the cellular network 16 are synchronized,
and a modem link is established. At least two attempts are made to establish the modem
link. Once the modem link is established, the cordless cellular base station 10 sends
an authorization request message in step 68. The authorization request message includes
the electronic serial number of the cordless cellular base station for identification
purposes. The network verifies that the cordless cellular base station 10 which is
identified by the electronic serial number is calling from the landline number which
was given to the cellular network when the cordless cellular base station was purchased.
Preferably, the cordless cellular base station uses the (CNI) calling number identification
feature of the telephone line from the PSTN 15 to verify that the call that is being
received is, in fact, on the landline 14 that was stored in the regional cellular
system. If the landline number on which the modem link is established is the same
as the stored landline number, the cellular network 16 accepts an initial authentication
message (AUTH) from the cordless cellular base station 10 and sends an initial authorization
message (auth) to the cordless cellular base station 10 in step 72. The cellular network
16 downloads certain operational parameters for the cordless cellular base station
10 in the authorization message. In the preferred embodiment the authorization message
comprises (a) Primary MIN; (b) CCBS-ID ― Password to be used by the CCBS in subsequent
communication with the CCBS VLR; (c) Public SID (SID) ― the System Identification
in which this CCBS should be operating; (d) Residential SID (RSID) ― the Residential
System Identification which should identify this CCBS; (e) CCBS_Auth_Count - the initial
value to use for fraud protection; (f) Registration/Deregistration Flag - an indication
to the CCBS which registrations and deregistrations for which the CCBS VLR would like
to be informed; (g) Authorization Frequencies - a list of frequencies within which
the cellular base station is authorized to operate; (h) Remote Network Update Number
1 (EtNllN1) ― the number which the CCBS should use for further communication with
the CCBS; (i) Remote Network Update Number 2 (RNUN2) ― the alternate number which
the CCBS should use if the Remote Network Update Number 1 no longer works; (j) LLN
― the land line number on which this CCBS should be operating, (k) SOC ― the system
operator code for the cellular provider; (1) Authorization Power ― the authorized
operating power level; (m) Transmitted Signal Strength - the maximum signal strength
for which this CCBS should operate; and (n) Receive Signal Strength ― the minimum
signal strength for which this CCBS will consider a mobile set channel. The operating
frequencies are, in a preferred embodiment, a portion of the frequencies in the cellular
spectrum. However, the operating frequencies may include all of the frequencies in
the cellular spectrum. The authorization power level is the power level at which the
CCBS is authorized to operate. In one embodiment, the user has the option of the level
of service that he or she wants to receive and could be changed a different fee for
a different level of service. For example, the user could choose either a lesser area
of coverage for the CCBS, a normal area of coverage for the CCBS or an expanded area
of coverage for the CCBS wherein each of these coverage areas would have a corresponding
authorization or authorized power level. Depending upon the level of service requested
by the user, the corresponding authorized power level will be sent to the CCBS in
the authorization message. The parameters received during the authorization step (auth)
are stored in the memory of the cordless cellular base station 10 and are used for
operation. Preferably, the parameters are stored in an EEPROM. The cordless cellular
base station 10 confirms the receipt of the auth message by sending a return result
message to the cellular network 16 in step 74. Once the return result message is received
and the initialization procedure is complete, either the cordless cellular base station
10 or the cellular network 16 releases the call (Release call) in step 76. If any
of the above attempts to initialize the cordless cellular base station 10 fail, the
initialization procedure is canceled by the cellular network 16 and, the authorization
step is reattempted after a certain period of time. If the second attempt fails, the
user can recontact the cellular network 16 by placing another call on the landline
14 to the cellular network 16 to request that the initialization procedure be tried
over again.
[0063] After the network authorization is complete, the cellular network 16 retains a permanent
record of the cordless cellular base station's unique identification password number,
the mobile station ID number of the primary mobile station 12 associated with the
cordless cellular base station 10 and the landline number that is associated with
the cordless cellular base station 10. In one embodiment, once the cordless cellular
base station 10 has completed a successful network authorization procedure with the
cellular network 16, an indicator on the cordless cellular base station 10 is illuminated
to signify that the cordless cellular base station 10 is authorized for use.
[0064] In an alternate embodiment, the network authorization procedure is similar to that
described above, except that the user initiates the authorization procedure by calling
the cellular network authorization phone number on the user's standard telephone landline
14 and providing the cellular network 16 with the landline number (LLN) to which the
cordless cellular base station 10 is connected. The cellular network (CN) 16 initiates
the telephone call (Initial Call) to the landline number on the public switched telephone
network (PSTN) 15 to which the cordless cellular base station 10 is connected. The
user does not answer the telephone call; instead, the landline communications hardware
29 (Figure 3) on the cordless cellular base station 10 is allowed to answer the call.
After a telephone link between the cordless cellular base station 10 and the cellular
network 16 has been established, the authorization procedure proceeds as described
above, by setting up a modem link and following the flow outline in Figure 7.
Cordless Cellular Base Station Registration List
[0065] As the number of cordless cellular base station users increase it will become more
and more likely that cordless cellular base stations 10 will be present in adjoining
houses. In such cases, it is not desirable to enable automatic registration for all
mobile stations 12 that come into proximity with a cordless cellular base station
10. Advantageously, the preferred registration scheme allows the cordless cellular
base station 10 to be accessible only to users who have been previously been granted
the registration privilege. The cordless cellular base station 10 maintains a cordless
cellular base station registration list 113 in a semipermanent portion of the memory
21 (Figure 3) which stores the mobile system identification number of the mobile stations
12 which have been previously been granted registration privileges with the cordless
cellular base station 10. By requiring preregistration of mobile stations 12, before
automatic registration occurs, accidental automatic registration with a nearby cordless
cellular base station 10 is prevented, however the convenience of automatic registration
for frequent users is still available.
[0066] As illustrated in Figure 8, the cordless cellular base station registration list
113 is preferably broken down into first and second parts 114, 115. The mobile station
identification numbers MINS of the "primary" mobile stations 12 which are granted
automatic registration privileges with the cordless cellular base station 10 are stored
in the first part 114 of the list 113. The primary users are the owners of the cordless
cellular base station 10 and are normally the users who are billed for the services
of the cordless cellular base station 10. The mobile station identification numbers
MIN of the "non-primary" mobile stations 12 most recently registered with the cordless
cellular base station 10 are stored in the second part 115 of the list 113. In the
preferred embodiment, the cordless cellular base station 10 is advantageously capable
of granting automatic registration privileges to a limited number of mobile stations
12 whose MINs are stored in the cordless cellular base station registration list 113.
Preferably, the cordless cellular base station 10 is capable of granting registration
privileges to two primary users and eight non-primary users. However, depending upon
the preferred use, the numbers could be less than or greater than those indicated
above.
[0067] The primary users in the first part 114 of the list are preferably not changeable
without intervention by an authorized agent or by communication with the regional
cellular network 16. The second part 115 of the list 113 listing the non-primary mobile
stations most recently granted automatic registration privileges is advantageously
maintained in order of most recent registration to the cordless cellular base station
12. Thus, if the second part 115 of the list 113 is already full, the last non-primary
mobile station on the list, i.e., the mobile station least recently granted automatic
registration, is deleted from the list 113 and a new mobile station is granted automatic
registration privileges and is placed at the top of the second part 114 or non-primary
registration list.
[0068] The cordless cellular base station 10 may also advantageously provide an LCD display
of the second part 114 of the list 113 listing the non-primary mobile stations 12
most recently granted automatic registration privileges. In this embodiment, the user
depresses a function key on the cordless cellular base station to display the second
part 114 of the list 113 listing the non-primary mobile stations. Once the second
part 114 of the list 113 is displayed, the user scrolls through the list of displayed
mobile station identification numbers to select a number that he would like to delete.
The user then depresses a function key labeled delete on the cordless cellular base
station 10 or in an alterative embodiment can enter a series of keys such as, 335#,
on the keypad of the cordless cellular base station 10 to delete the highlighted numbers
from the second part 115 of the automatic registration list 113.
[0069] For each entry, the cordless cellular base station registration list 113 stores a
status record 116 that indicates the state of the mobile station with respect to the
cordless cellular base station and a mobile station identification number record 117.
Preferably, there are three states of a mobile station 12 with respect to the cordless
cellular base station 10 which are referred to as the: "standby", "active" and "dominant"
states. The dormant state, shown by a "D" on the table 113, indicates that the mobile
station 12, which has previously registered with the cordless cellular base station
10, is not currently registered with the cordless cellular base station 10. The standby
state, which is indicated by a "S" on the table 113, indicates that the mobile station
12 is currently registered with the cordless cellular base station 10 and is not currently
on a call, i.e., the mobile station 12 is "standing by" waiting to receive or place
a call through the cordless cellular base station 10. The active state, which is shown
by an "A" on the table 113, indicates that the mobile station 12 is registered with
the cordless cellular base station 10 and is currently on a call which is being controlled
by the cordless cellular base station 10. As indicate above, in the preferred embodiment,
up to two mobile stations 12 may be listed as active at a time.
Initial Registration
[0070] When a user wants to use a mobile station 12 which was not previously registered
with the cordless cellular base station 10, the following initial registration procedure
is performed described as follows with reference to Figures 9 and 10. Figure 9 shows
the messages which are passed between the mobile station 12 and the cordless cellular
base station 10. Figure 10 shows the process which takes place in the cordless cellular
base station 10 to enable the initial registration. In step 119 of Figure 9, the user
presses the initial registration button 111 (Figure 2) on the cordless cellular base
station 10. In the flow chart of Figure 10, at action block 120 the depression of
the initial registration button is detected and control passes to action block 121.
At action block 121, the cordless cellular base station 10 sets a new registration
(new-reg) timer. Preferably, the new registration timer is set for 30 seconds.
[0071] After the initial registration button 111 on the cordless cellular base station 10
is depressed, the user of the mobile station 12 activates a test registration procedure
on the mobile station in step 109. In a preferred embodiment, the test registration
procedure is activated by the user depressing a test registration function key on
the mobile station 12. In an alternate embodiment, the user may depress a series of
specified keys on the mobile station keypad, such as 878#, to initiate the test registration
procedure on the mobile station 12. The initiation of the test registration function
causes the mobile station 12 to measure the received signal strength s-n each channel
and to store the measurement. The mobile station then checks the channels which have
the strongest receive signal strength to determine if a digital control channel (DCCH)
is present. If a DCCH is not present, the mobile station checks the channel with the
next highest receive signal strength. If a DCCH is present, the mobile station checks
to see if its system ID identifies it as a private system. If it is a private system,
the mobile station tries to register with the device by sending out a test registration
message (TR) in step 122 of Figure 9. The test registration message is specified by
the IS-136 standard.
[0072] At decision block 123 of Figure 10, the cordless cellular base station 10 checks
to see if the test registration message is received from a mobile station 12. If the
test registration message is received, control passes to decision block 124. If the
test registration message is not received control passes to decision block 125, where
the cordless cellular base station checks to see if the new registration timer (new-reg)
has expired. If the timer has not expired, control returns to decision block 123.
If the timer has expired, the initial registration attempt is completed.
[0073] At decision block 124, the cordless cellular base station 10 determines if the registration
list of Figure 8 is full. If there is still room in the registration list, control
passes to action block 126. If the registration list is full, control passes to decision
block 127. At decision block 127, the cordless cellular base station 10 determines
if the status of one of the non-primary mobile stations 12 in the registration list
is indicated as being dormant. If the status of one of the non-primary mobile stations
12 is indicated as being dormant, control passes to action block 128. If none of the
non-primary mobile stations 12 is listed as being dormant, control passes to action
block 129. At action block 129, a negative test registration response is sent to the
mobile station and the initial registration process is abandoned. At action block
128, the non-primary mobile station 12 with the longest inactivity time is removed
from the registration list and control passes to action block 126. In the preferred
embodiment, the non-primary mobile station with the longest inactivity time would
be the last non-primary mobile station on the registration list.
[0074] At action block 126, the mobile station identification number of the requesting mobile
station is added to the registration list. Next, at action block 130, the cordless
cellular base station 10 sends a positive test registration response message (TRR)
to the mobile station 12 and control passes to decision block 133.
[0075] The transmission of the positive or negative test registration response from the
cordless cellular base station to the mobile station is shown in step 131 of Figure
9. If a negative test registration response, or no test registration response is received
at the mobile station, the mobile station will check the channel with the next highest
receive signal strength and repeat the procedure indicated above to try to determine
if it is a private system, and if so, to try to register with the device by sending
out a test registration message (TR).
[0076] Upon receiving the positive test registration response, in accordance with the IS-136
standard, the mobile station 12 will display a set of alpha characters transmitted
by the cordless cellular base station 10 in the test registration message. In the
preferred embodiment, the alpha characters which are displayed form the word "cordless",
at which time the mobile station may decide to accept or reject the cordless registration
with the cordless cellular base station. If the user wishes to accept the registration,
he depresses a specified series of keys on the keypad, such as 9#. If the user accepts
the registration, the mobile station sends a registration message (R) in step 132
of Figure 9 to the cordless cellular base station. If the user wishes to reject the
registration, the user depresses another specified series of keys on the keypad, such
as 6# or in another embodiment does not depress any keys. If the registration is rejected,
no message is sent to the cordless cellular base station 10.
[0077] In the meantime, at decision block 133, the cordless cellular base 10 checks to see
if a registration message has been received from the mobile station. If a registration
message (R) is received, control passes to action block 134. If a registration message
(R) was not received control passes to decision block 135 where the cordless cellular
base station 10 checks to see if the new_reg timer has expired. If the new_reg timer
has not expired, control returns to decision block 133 where the cordless cellular
base station will continue to check for the receipt of the registration message (R)
from the mobile station. If the new_reg timer has expired without the cordless cellular
base station 10 receiving a response from the mobile station 12, control passes to
action block 136 where the initial registration attempt is canceled.
[0078] At action block 134, the new_reg timer is stopped and control passes to action block
137. At action block 137, the cordless cellular base station sends a registration
accept message (RA) to the mobile station as is shown in step 138 of Figure 9 and
control passes to action block 139. At action block 139, the status of the mobile
station 12 is updated as being in standby mode and the initial registration procedure
is completed. At action block 140, the cordless cellular base station 10 proceeds
with the network update attempt procedure as described in association with Figure
13 below.
[0079] After the mobile station 12 has completed the initial registration with the cordless
cellular base station 10, the mobile station 12 will automatically register with the
cordless cellular base station 10 without the need to go through the initial registration
procedure. Thus, when a mobile station 12 comes within range of a cordless cellular
base station 10 with which it has been granted automatic registration privileges and
the mobile station 12 is not currently handling a call, in accordance with the preferred
embodiment, the mobile station 12 automatically switches from regional cellular service
mode to cordless telephone landline service mode without user intervention. The automatic
registration of the mobile station 12 with the cordless cellular base station 10 is
discussed in more detail below.
Automatic Registration of a Mobile Station with a Cordless Cellular Base Station
[0080] The mobile station 12 only attempts to locate a cordless cellular base station 10
when the mobile station 12 is not currently handling a call. When a mobile station
12 that is not currently handling a call comes into the range of a cordless cellular
base station 10 with which it has been granted automatic registration privileges,
the mobile station 12 preferably automatically deregisters from the cellular network
and registers with the cordless cellular base station 10. The cordless cellular base
station 10 advantageously is able to communicate with up to two mobile stations 12
at one time. The cordless cellular base station 10 displays an indication of whether
its digital control channel (DCCH) is supporting one or more mobile stations 12. In
a preferred embodiment, the cordless cellular base station 10 displays the mobile
identification number of each mobile station 12 that the cordless cellular base station's
digital control channel (DCCH) is currently supporting. The cordless cellular base
station 10 remains ready to receive registrations and other legitimate requests from
the mobile stations 12 at any time.
[0081] In general, the range in which automatic registration with the cordless cellular
base station 10 is achievable is dictated by the strength of the transmission signal
from the cordless cellular base station 10. Preferably, the cordless cellular base
station 10 is capable of transmitting an approximately 6.3 mW signal. This translates
into an automatic registration range for the cordless cellular base station 10 of
approximately 500-1,000 feet. The variation in the registration range is due to the
values broadcast on the DCCH of the cordless cellular base station, variations in
weather conditions, surrounding EMI interference, and sizes and layouts of the buildings
in which the cordless cellular base station 10 may be located.
Location of the Cordless Cellular Base Station by a Mobile Station
[0082] As illustrated in Figure 10, when the mobile station 12 is being served by a control
channel and is not currently handling a call, the mobile station 12 searches for the
presence of the cordless cellular base station 10 after each selection of a new control
channel. Once a new channel is selected, at decision block 140 the cordless cellular
base station checks to see if a new digital control channel is selected. If at decision
block 140, a new digital control channel is acquired, control passes to action block
142. If at decision block 140, a new digital control channel is not acquired, control
passes to decision block 141. If at decision block 141 a new analog control channel
is acquired, control passes to action block 142. If at action block 141 a new analog
control channel is not acquired, control returns to decision block 140.
[0083] At action block 142, the current extended Public Service Profile of the mobile station
12 is compared to all the stored extended Public Service Profiles in the table 78
(Figure 6) in the mobile station for each of cordless cellular base stations 10 that
are stored. For an analog control channel, the extended public service profile preferably
contains the CC, SID, ACCH channel number and DCC for the control channel as described
above. For a digital control channel, the extended Public Service Profile preferably
contains the CC, SID, DCCH channel number, and DVCC as described above. If at decision
block 144 there is an extended PSP match, control passes to action block 146. If at
decision block 144, there is no extended PSP match, control passes to action block
148.
[0084] At action block 146 once an extended PSP match is made, it is possible that the mobile
station 12 is within the vicinity of a cordless cellular base station 10 with which
it has previously registered. As known to those of skill in the art, the mobile station
12 is provided with a list of frequencies by the cellular network 16 called a neighbor
list (NL). As known to those of skill in the art, the neighbor list is a list of frequencies
that the neighboring cells operate on and assists the mobile station in selecting
nearby cells for control when the signal strength of the current cell is no longer
optimal. In a typical mobile station 12, the mobile station scans the channels on
the neighbor list to determine if a control channel which is stronger than its current
control channel can be located on the channels of the neighboring cells. Once a clearer
channel is located, the mobile station automatically "camps onto" the new control
channel. Thus at action block 146 when an extended PSP match is made, the mobile station
12 advantageously adds the stored primary and alternate cordless cellular base station
frequencies that the digital control channel (DCCH) of the cordless cellular base
station 10 was detected on, i.e., f
0, f
1, f
2, f
3, for each row in the table 78 (Figure 6) on which an extended PSP match was found,
to the Neighbor List (NL) forming an extended neighbor list (ENL). Thus, at action
block 148, each of the frequencies of the neighbor list are sequentially scanned to
determine if a clearer control channel can be located. If on one of the frequencies
of the neighbor list that the mobile station is scanning, a private system identifier,
such as the RSID of the cordless cellular base station, is detected, in accordance
with the IS-136 standard, the mobile station 12 synchronizes with that control channel
and checks to see if this is an identifier that the mobile station recognizes. At
decision block 150, the mobile station compares the identifier that is obtained for
the control channel with the extended RSID for the cordless cellular base station
that it is scanning for. As described above, an extended RSID is preferably a country
code (CC), a System Operator Code (SOC), and a 16-bit Residential System ID (RSID)
for the cordless cellular base station 10. If an extended RSID match is detected,
control passes to action block 154. If an extended RSID match is not detected, control
passes to action block 152 where the mobile station checks to see if the signal strength
of any of the frequencies on the neighbor list is strong enough to warrant a channel
change. If at decision block 148 the signal strength of one of the channels is strong
enough to select a new channel, control returns to decision block 140. If at decision
block 152 none of the channels are strong enough to warrant a channel change, control
returns to action block 148 where the channels on the neighbor list are continually
scanned.
[0085] At action block 154, the mobile station deregisters from the regional cellular network.
Control passes to action block 156 where the mobile station attempts to register with
the cordless cellular base station 10 using the CCBS registration procedure described
below in association with Figure 12. If registration succeeds, the mobile station
camps on the cordless cellular base station's Digital Control Channel (DCCH).
Automatic Registration of a Cordless Cellular Base Station (CCBS)
[0086] When the mobile station 12 has determined that it is in proximity with the cordless
cellular base station 10 using the procedures described above, the mobile station
12 attempts to register with the cordless cellular base station 10 using the procedure
illustrated in Figure 12. Initially, at decision block 158 the cordless cellular base
station 10 checks to see if the mobile station identification number (MIN) of the
mobile station 12 matches a MIN stored in the automatic registration list in the cordless
cellular base station 10. If the MIN of the mobile station matches one of the stored
MINs, control passes to action block 160. If the MIN of the mobile station 12 does
not match one of the stored MINs, control passes to action block 162. At action block
162, the automatic registration attempt is rejected and control passes to action block
164 where the automatic CCBS registration procedure is terminated.
[0087] At action block 160, the automatic registration attempt of the mobile station 12
is accepted. Next, at decision block 166, the cordless cellular base station 10 checks
the status of the mobile station in the registration list of Figure 8. If the mobile
station 12 is listed as dormant, i.e., not in active or standby modes, control passes
to action block 172. If the mobile station 12 is not listed as dormant, control passes
to action block 168. At action block 168, the automatic CCBS registration procedure
is considered to be completed and control passes to action block 170 where the automatic
CCBS registration procedure is terminated.
[0088] At action block 172, the status of the mobile station 12 is updated as being in standby
mode. At action block 174, the automatic CCBS registration procedure is considered
to be completed and control passes to action block 176. At action block 176, the cordless
cellular base station 10 proceeds with the network update attempt procedure as described
in association with Figure 13 below.
Network Update Attempt
[0089] Figure 13 illustrates the network update attempt procedure that the cordless cellular
base station uses to contact the cellular network to inform it of a recent mobile
station registration. At decision block 190, the state of the landline 14 associated
with the cordless cellular base station 10 is checked to determine if the network
call forwarding procedure can be initialized. If at decision block 190, the state
of the landline 14 is idle, control passes to action block 192, where the Network
Call Forwarding Procedure as described in association with Figures 14a and 14b is
initiated. If at decision block 190, the state of the landline 14 is not idle, control
passes to decision block 194. At decision block 194, the state of the landline is
checked to determine if it is busy. If the landline 14 is busy, control passes to
decision block 195. If the land line is not busy control passed to decision block
196. At decision block 196, the state of the land line is checked to determine if
the landline is ringing. If the land line is not ringing, control passes to action
block 195. If the land line is ringing, control passes to decision block 198. At decision
block 198, the state of the voice channels for the first and second mobile stations
of the cordless cellular base station are checked to see if there is room to add the
mobile station onto the ringing call. If both channels are busy, for example, an intercom
call between two mobile stations is in progress, control passes to action block 195.
If both channels are not busy, control passes to action block 200. At action block
200, the newly added mobile station is paged, in a manner known to those of skill
in the art, and can be added on to the present ringing call if the user presses the
send key on the mobile station 12. Whether the mobile responds or not, control passes
to action block 195.
[0090] At action block 195, the Network Call Forwarding Procedure is queued until the cordless
cellular base station and the landline are both free and are able to initiate the
network call forwarding procedure. The network call forwarding procedure is described
below in association with Figures 14a and 14b.
Post-Mobile Station Registration
[0091] After the mobile station 12 is registered and referring back to Figure 6, for a new
non-primary cordless cellular base station, for a cordless cellular base station that
was not previously on the list, the mobile station 12 places the data for this cordless
cellular base station 10 in the most recent non-primary cordless cellular base station
row 84, just below the row for the primary cordless cellular base station 82. The
data for the previous most recent non-primary cordless cellular base station is moved
to the next most recent non-primary cordless cellular base station row 86. The row
for the least recently used non-primary cordless cellular base station, i.e., the
previous next most recent cordless cellular base station row, may be lost. For the
most recent nonprimary cordless cellular base station row 84, the mobile station 12
places the data regarding the cellular network that it just deregistered from into
the table 78. If the cordless cellular base station was already included on the list,
the new information simply replaces the information in the old row. The mobile station
12 places the current Country Code in the CC cell, the current System Operator Code
in the SOC cell, and the current System Identifier in the SID cell the most recent
row as collected from the cordless cellular base station. In addition, the public
service profile for the mobile station is inferred from the broadcast neighbor list
that is received from the cordless cellular base station 10 as described above.
[0092] When the mobile station 12 has registered with the cordless cellular base station
10, the mobile station 12 functions as a cordless telephone mobile station, referred
to as operating in the cordless telephone landline service mode. In the cordless mode,
the mobile station provides basic and enhanced telephone services over the landline
connected to the cordless cellular base station 10. The mobile station supports the
enhanced telephone services that are provided by the land network services when it
operates in cordless mode, such as call waiting, three-way calling, party line service
(i.e., enabling multiple landline numbers to access a single landline), and distinctive
ringing services (i.e., different ringing patterns based on the incoming calling number).
Network Call Forwarding
[0093] After a successful registration of the mobile station 12 with the cordless cellular
base station 10, in a preferred embodiment the cordless cellular base station 10 sends
a call forwarding update message to the cellular network 16 requesting that the cellular
network 16 route all calls for the mobile station identification number of the registered
mobile station 12 to the landline number associated with the cordless cellular base
station 10. As indicated above, the CCBS VLR informs the cordless cellular base station
during the initial authorization message of which types of registration/deregistration
activities the CCBS VLR would like to be informed. For example, some of the types
of registrations/deregistrations that the CCBS VLR may want to be informed of include:
power down registration, power up registration, location area, forced registration,
periodic registration, deregistration, new system registration, ACC to DCCH, or TMSI
timeout. In the case when the CCBS VLR wants to be informed of a location area registration,
the location update or call forwarding procedure as illustrated in Figure 14a is executed.
The cordless cellular base station (CCBS)10 dials the stored remote network update
number via the PSTN 15 (the cordless cellular base station (CCBS)10 tries the Remote
Network Update Number 1 first and if it is busy it tries the Remote Network Update
Number 2) in a network contact calling step 202 (Network Contact Update Call) to contact
the cellular network (CN) 16. The cellular network 16 upon answering the call sets
up a modem link in step 206. In an authentication step (AUTH) 208, the cordless cellular
base station 10 starts an authorization timer and sends an authentication message
to the cellular network 16 which includes the mobile system identification number
to be updated, the cordless cellular base station identification number and a cordless
cellular base station authorization count. The cordless cellular base station authorization
count maintains a running count of the number of updates the cordless cellular base
station 10 has made over this landline number as a fraud prevention mechanism. The
cellular network 16 compares the call number ID (CNI) from the PSTN 15 for the landline
number of the cordless cellular base station 10 which made the call with the landline
number of the cordless cellular base station 10 stored in a data base on the cellular
network 16 and verifies that the mobile system identification number to be updated,
the cordless cellular base station identification number and a cordless cellular base
station authorization count provided by the cordless cellular base station 10 match
the stored values in the cellular network 16. Once the authentication message is processed
and validated, a return result message is sent to the cordless cellular base station
10 in step 210 and the cordless cellular base station authorization count is updated.
Further, the cellular network sets a message receive timer to see if the cordless
cellular base station 10 is going to send it a message in a specified time period.
If the authentication message can not be validated, i.e., if any of the above-referenced
values do not match, the cellular network 16 breaks the modem connection, releases
the call, and exits the procedure.
[0094] In the meantime, the cordless cellular base station 10 is waiting to receive the
return result message from the cellular network 16. If the return result message is
not received during the authentication timer period or if an error result is received,
the cordless cellular base station 10 will process the error and may attempt a new
connection with the cellular network 16 after a specified period of time has elapsed.
[0095] After receiving the return result message, the cordless cellular base station 10
stops the authentication timer, starts a location update timer and sends a location
update message to the cellular network 16 in step 212 via a modem link. In a preferred
embodiment, the location update message comprises the mobile station identification
number (MIN) of the registered mobile station 12 for which the calls are to be forwarded
and the landline number to which the cordless cellular base station 10 is connected.
The cellular network 16 receives the location update information from the cordless
cellular base station 10, verifies that it agrees with the stored parameters in the
cellular network 16, and stops the message receive timer. If the parameters received
from the cordless cellular base station 10 do not agree with the stored parameters
in the cellular network 16, the cellular network 16 sends an error message to the
cordless cellular base station 10 and resets the message receive timer. If the message
receive timer expires and no message has been received from the cordless cellular
base station 10, the cellular network 16 resends the return result message, resets
the message receive timer one more time, and waits for a response. If after two timeouts,
no message has been received from the cordless cellular base station 10, the network
16 breaks the modem connection, releases the call, and exits the procedure. If the
parameters received from the cordless cellular base station 10 agree with the stored
parameters in the cellular network 16, the cellular network 16 updates the information
stored in the cordless cellular base station visitor location register (CCBS VLR)
regarding the mobile station location and sends a return result message in step 214
to the cordless cellular base station 10 over the modem link to verify the receipt
of the information.
[0096] In the meantime, the cordless cellular base station 10 is waiting to receive the
return result message from the cellular network 16. If the return result message is
not received during the location update timer period or if an error result is received,
the cordless cellular base station 10 will process the error and may attempt to resend
the location update message after a specified period of time has passed. Once the
return result message has been received by the cordless cellular base station 10,
the location update timer is stopped. The cellular network 16 ends the call forwarding
update procedure and either the cellular network 16 or the cordless cellular base
station 10 releases the call (Release call) in step 220.
[0097] Figure 14b illustrates an alternate embodiment of the call forwarding procedure,
which is the same as the procedure in Figure 14a from steps 202-212. After the location
update message is received, the information in the message has been compared with
the stored parameters and matches, and the network updates the information regarding
the location of the mobile station, the cellular network checks to see if it needs
to send an updated authorization message to the cordless cellular base station 10.
If the cellular network needs to send an authorization message, instead of sending
the return result message 214 as in Figure 14a, the cellular network 16 sends the
cordless cellular base station authorization message which includes the cordless cellular
base station identification number and a list of authorized or operational parameters
including operational frequencies, which is the same as the initial authorization
message described above, and sets a return result timer.
[0098] If the location update timer expires and no message have been received from the cellular
network 16, cordless cellular base station 10 resends the location update message,
resets the timer, and waits for a response. If after two timeouts, no message have
been received from the cellular network 16, the cordless cellular base station 10,
breaks the modem connection, releases the call, and exits the procedure. If an invalid
authorization message is received, the cordless cellular base station 10 sends an
authorization error message to the cellular network, resets the timer and may wait
for the receipt of a new authorization message.
[0099] If a valid authorization message is received by the cordless cellular base station
10 in step 216 over the modem link, the cordless cellular base station 10 updates
its operational parameters as received in the message and stops the authorization
timer. The cellular network 16 is able to prevent the cordless cellular base station
10 from operating by removing all of its operational frequencies in the cordless cellular
base station authorization message. This is a simple way to cancel the service of
an unauthorized user. In addition, the network 16 may update the operational parameters,
of the cordless cellular base station 10 with the cordless cellular base station authorization
message. For example, the cellular network 16 may update the list of operational frequencies
of the cordless cellular base station 10, if it is determined that an insufficient
number of clear frequencies have been provided to the cordless cellular base station
10. The cordless cellular base station 10 confirms the receipt of the authorization
message by sending a return result message to the cellular network 16 in step 218.
If the cellular network does not receive the return result message before its return
result timer expires, the cellular network 16 resends the CCBS authorization message,
resets the return result timer, and waits for a response. If after two timeouts a
return result has not been received from the cordless cellular base station 10, the
cellular network 16 cancels the call forwarding update, breaks the modem connection,
releases the call, and exits the procedure. If the return result message is received,
the cellular network 16 ends the call forwarding update procedure and either the cellular
network 16 or the cordless cellular base station 10 releases the call (Release call)
in step 220.
[0100] After the call forwarding update process is complete, the cellular network 16 routes
all calls for the mobile station identification number of the registered mobile station
12 to the landline number associated with the cordless cellular base station 10. As
illustrated in Figure 15, the cellular network 16 can be broken down into the following
components: the mobile switching complex (MSC) 222, the home location register (HLR)
224, a traditional visitor location register (VLR) 226 and the cordless cellular base
station visitor location register (CCBS VLR) 228. The mobile switching complex 222,
home location register 224 and visitor location register 226 are generally the same
as the components that generally exist currently in a standard cellular network, as
known to those of skill in the art. The present invention adds the CCBS VLR 228 which
is a data base that stores the location, i.e., landline number, of the mobile stations
which are being controlled by the cordless cellular base station (CCBS)10.
[0101] When the cordless cellular base station 10 calls the cellular network 16 in step
230, it is communicating with the CCBS VLR 228 to provide the information regarding
the location update and location update cancel requests. When the location update
request is received by the CCBS VLR 228, the CCBS VLR 228 sends a REG NOT INVOKE message
in step 232 to the HLR 224 associated with the mobile station to inform the HLR 224
that the information for routing calls for that particular mobile station identification
number is available from the sending CCBS VLR 228. The HLR 224 responds in step 234
with a REG NOT RETURN RESULT message indicating that it has received and accepted
the location update message.
[0102] When a call is originated by dialing the mobile station identification on the PSTN
15, the call is sent to the MSC 222 in step 236. The originating MSC 222 sends a LOCATION
REQUEST message to the mobile station's HLR 224 in step 238. The HLR 224 recognizes
that the location of the mobile station- is being controlled by the CCBS VLR 228 which
contacted it earlier. In step 240, the HLR 224 constructs a ROUTING REQUEST message
and sends it to the CCBS VLR 228 that provided the earlier REG NOT INVOKE message
providing an update of the mobile's location. THE CCBS VLR 228 locates a TLDN for
the landline that the cordless cellular base station is connected to and returns this
information to the HLR 224 in a ROUTING REQUEST RESPONSE message in step 242. The
HLR 224 adds the MIN and the ESN of the mobile station to the routing information
and returns a LOCATION RESPONSE message to the originating MSC 222 in step 244. The
MSC 222 places the call over the PSTN 15 and the call is delivered to the landline
number for the cordless cellular base station 10 that is routing the calls for the
mobile station. The cordless cellular base station 10 pages the mobile stations 12
listed in standby mode as indicated below and the PSTN 15 rings the extension phones
attached to the landline number in step 246, thus completing the call forwarding process.
If there are two or fewer mobile stations listed in standby mode, the cordless cellular
base station pages the mobile station in a conventional manner as a regional cell
would page a mobile station, i.e., providing the digital control channel information
and the calling number information to enable the mobile station to answer the call
if the send button is depressed. If more than two mobile stations are listed in standby
mode, all of the mobile stations receive an alert message which enables the phones
to ring, but does not include the digital traffic channel information to answer the
call. In this case, the cordless cellular base station listens for the first mobile
station to depress the send button. The cordless cellular base station will send that
mobile station the digital traffic channel information which will enable the mobile
station to answer the call. In another embodiment, if the primary user is listed as
being in standby mode, the primary user will always be paged with the digital control
channel information to answer the call and the remaining mobiles listed as being in
standby will be sent the alert message and will ring If the primary user presses the
send button first, the call will be answered immediately. If one of the other mobile
stations presses the send button first, the primary user will be unable to answer
the call immediately. The cordless cellular base station will send the first responding
mobile station the digital traffic channel information. Upon receiving the digital
traffIc channel information, the other mobile station will be able to answer the call.
Automatic Contact of the Cordless Cellular Base Station by the Cellular Network
[0103] In order to enable the cellular network 16 to periodically change the operational
parameters of the cordless cellular base station 10, cordless cellular base station
10 preferably includes a preset timer which counts down the amount of time since the
cordless cellular base station 10 last contacted the cellular network 16. When the
timer expires, the cordless cellular base station 10 automatically contacts the cellular
network 16. In the preferred embodiment, the timer is set for thirty days; thus if
the cordless cellular base station 10 has not contacted the cellular network 16 within
thirty days, for example, to request a location update for a registered mobile station,
the cordless cellular base station 10 automatically contacts the cellular network
16. In response the cellular network determines if it is necessary to send the cordless
cellular base station a new authorization message. If a new authorization message
is required, the cellular network sends the message to the cordless cellular base
station. If a new authorization message is not required, the cellular network sends
a return result message to the cordless cellular base station. Upon receiving either
message from the cellular network, the timer in the cordless cellular base station
is reset for thirty days. This feature is advantageous for several reasons.
[0104] First, this enables the cellular network 16 to regularly update the operational parameters
in the cordless cellular base station 10 to accommodate changes in the service in
the area around the cordless cellular base station 10 and to update the cordless cellular
base station on any changed features of the cellular network 16. For example, the
cellular network 16 may temporarily alter the telephone number that the cordless cellular
base Station 10 calls to access the location update/call forwarding feature.
[0105] In addition, this feature is useful in preventing fraudulent usage of a cordless
cellular base station 10. For example, if the owner did not pay the bill for the service
and also stopped using the cordless cellular base station 10 or kept the mobile stations
exclusively at home but continued the use of the CCBS, it would be difficult for the
cellular network 16 to remotely cancel the operation of the cordless cellular base
station 10, because the cordless cellular base station 10 may not ever contact the
cellular network 16. With the automatic contact feature, the cellular network 16 would
automatically contact the cordless cellular base station 10 every thirty days. The
network 16 could then send a new authorization message removing all of the operating
frequencies from the cordless cellular base station which belonged to the non-paying
customer, thus making the cordless cellular base station 10 inoperable.
Call Initiation and Reception
[0106] Referring back to Figure 1-2, when a call is initiated by a registered mobile station
12 that is in the standby mode, the cordless cellular base station 10 will process
the air interface transaction required to establish a cellular originated call and
connect it to the landline service. Before connecting the call to the land line 14,
however, the cordless cellular base station 10 preferably checks first to see if the
phone number matches the MIN for one of the other mobile stations 12 which is listed
in standby mode in the registration table 113 (Figure 8) on the cordless cellular
base station 10. If the phone number matches a MIN for the one of the mobile stations
12 listed in standby mode, the cordless cellular base station 10 pages that mobile
station 12 and initiates an intercom conversation between the two mobile stations.
The intercom feature is described in more detail below. The intercom conversation
does not make the landline 14 busy, so the wireline extensions connected to the landline
14 can initiate and receive calls over the landline 14 associated with the cordless
cellular base station 10.
[0107] If one of the mobile stations calls the landline number associated with the cordless
cellular base station 10, only the mobile stations 12 listed as being in standby mode
will ring. This is for two reasons. First, the cordless cellular base station 10 does
not have the capability of ringing the phones associated with the landline 14 as the
ring signal for those phones are provided by the PSTN 15. Further, while it might
be possible to set the cordless cellular base station 10 up so it could call the other
land line extensions (e.g., by requiring that the CCBS be connected to two separate
PSTN lines), this would add some significant expense for very little additional value.
Thus, this is not a preferred embodiment.
[0108] When a call is received on the landline 14 associated with the cordless cellular
base station 10, all the extensions connected to the landline 14- ring and the cordless
cellular base station 10 pages all registered mobile stations 12 which are in the
standby state. The mobile stations 12 answer the call by pressing a send button on
the mobile station 12, the cordless cellular base station 10 transmits the voice signals
between the landline 14 and the mobile station 12. Any of the extensions associated
with the landline number 14 or any of the mobile stations 12 can answer the ringing.
[0109] If more than one mobile station 12 answers the call by pressing a send button on
a mobile station 12, the cordless cellular base station 10 bridges the call such that
each mobile station 12 acts as an "extension." In the preferred embodiment, the cordless
cellular base station 10 can bridge up to two mobile stations 12 on a single call.
If a third mobile station or more attempts to add to the call, the additional mobile
stations 12 are denied access to the cordless cellular base station 10 and are not
added to the call, thus remaining in standby mode. If at any time a call being handled
by the cordless cellular base station 10 is in progress and only one mobile station
is listed as being active, a second mobile station 12 in standby mode can be added
to the call by pressing the send button on the second mobile station 12. The ability
to bridge two calls requires sending two voice signals from the cordless cellular
base station 10 to the listener mobile stations 12, as described in more detail below
is association with Figures 16-18. If it would be desirable to add additional mobile
stations 12 beyond two mobile stations 12 to the same call, additional transceivers
could be added to the cordless cellular base station 10, as known to those of skill
in the art.
Bridging Two Calls on the Cordless Cellular Base Station
[0110] When there are two mobile stations 12 bridged by the cordless cellular base station
CCBS 10 to a call on the PSTN 15, the cordless cellular base station 10 is able to
match the functionality and performance of regular extension telephone operation.
Each mobile station 12 is able to receive the voice data from both the other mobile
station and the signals from the PSTN 15.
[0111] The preferred embodiment utilizes a system in which the sum of the mobile station
12 and the PSTN 15 voice signals are encoded. As shown in Figure 16, the cordless
cellular base station (CCBS) 10 utilizes a CODEC 250 which contains a VSELP speech
encoder (VSE) 252 and a VSELP speech decoder (VSD) 254 as known to those of skill
in the art. For simplicity, Figure 16 shows that two CODECs are used for the cordless
cellular base station 10. In the preferred embodiment, only a single CODEC 250 is
used and the transmission to/from each mobile station 12 is shifted in time, thus
enabling a single CODEC in the cordless cellular base station 10 to encode and decode
voice signals for both mobile stations 12. In the preferred embodiment, the communication
or voice signals from a first mobile station (MST) are digitally encoded by the VSELP
speech encoder (VSE) 252 and are preferably sent to the cordless cellular base station
10 using the IS-136 cellular communication protocol. The signal is received by the
cordless cellular base station 10 and is decoded by the VSELP speech decoder (VSD)
254 to a voice signal. The voice signal from the first mobile station is summed at
summer 256 with the voice signal that was received from the PSTN 15 and was coded
by the 2-wire to 4-wire hybrid device (H). The summed signal is then encoded by the
VSELP speech encoder (VSE) 252 into a digitally compressed signal which is sent to
the second mobile station (MS2) using the IS-136 cellular communications protocol.
The second mobile station decodes the digitally compressed signal using the VSELP
speech decoder (VSD) 254 to an audio voice signal for the listener to hear. In this
way, the user of the second mobile station is able to listen to the voices of both
parties on the PSTN 15 and on the first mobile station.
[0112] Similarly, the audio communication from the second mobile station (MS2) are digitally
encoded by the VSELP speech encoder (VSE) 252 and are sent to the cordless cellular
base station 10 using the IS-136 cellular communication protocol. The signal is received
by the cordless cellular base station 10 and is decoded by the VSELP speech decoder
(VSD) 254 to a voice signal. The voice signal from the second mobile station is summed
at summer 258 with the voice signal received from the PSTN 15 and encoded by the hybrid
device (H). The summed signal is then encoded by the VSELP speech encoder (VSE)252
into a digitally compressed signal which is sent to the first mobile station (MST)
using the IS-136 cellular communications protocol. The first mobile station decodes
the digitally compressed signal using the VSELP speech decoder (VSD)254 to an audio
voice signal for the listener to hear. In this way, the user of the first mobile station
is able to listen to the voices of both parties on the PSTN 15 and on the second mobile
station. The voice signal from the second mobile station is summed with the voice
signal received from the first mobile station and are encoded by the hybrid device
(H) for delivery to the user on the PSTN 15.
[0113] In a second embodiment, as shown in Figure 17, the cordless cellular base station
10 compares a voice signal from one mobile station with the voice signal from the
PSTN and whichever is louder is sent to the other mobile station. Similar to the embodiment
of Figure 16, the cordless cellular base station utilizes a CODEC 250 which contains
a VSELP speech encoder (VSE)252 and a VSELP speech decoder (VSD)254 as known to those
of skill in the art. For simplicity, Figure 17 shows that two CODECs are used by the
cordless cellular base station 10. In the preferred embodiment, only a single CODEC
250 is used and the transmission to/from each mobile station is shifted in time, thus
enabling a single CODEC in the cordless cellular base station to encode and decode
voice signals for both mobile stations. In the preferred embodiment, the communication
or voice signals from a first mobile station (MST) are digitally encoded by the VSELP
speech encoder (VSE)252 and are sent to the cordless cellular base station 10 using
the IS-136 cellular communication protocol. The signal is received by the cordless
cellular base station 10 and is decoded by the VSELP speech decoder (VSD) 254 to a
voice signal. The voice signal from the first mobile station is compared to the voice
signal that was received from the PSTN15 and was coded by the hybrid device (H) by
a voice level comparator (VLC) 260. The voice level comparator 260 selects which of
the two signals is louder and controls the operation of a switch 262 to enable the
louder of the two signal to pass to the VSELP encoder (VSE)250 for the second mobile
station (MS2) which is encoded into a digitally compressed signal which is sent to
the second mobile station (MS2) using the IS-136 cellular communications protocol.
The second mobile station decodes the digitally compressed signal using the VSELP
speech decoder (VSD) 254 to an audio voice signal for the listener to hear. In this
way, the user of the second mobile station is only able to listen to the voice of
the louder of the parties on the PSTN 15 and on the first mobile station.
[0114] Similarly, the communications or voice signals from a second mobile station (MS2)
are digitally encoded by the VSELP speech encoder (VSE) 252 and are sent to the cordless
cellular base station 10 using the IS-136 cellular communication protocol. The signal
is received by the cordless cellular base station and is decoded by the VSELP speech
decoder (VSD) 254 to a voice signal. The voice signal from the second mobile station
is compared to the voice signal that was received from the PSTN 15 and was coded by
the hybrid device (H) by a voice level comparator (VLC) 260. The voice level comparator
260 selects which of the two signals is louder and controls the operation of a switch
262 to enable the louder of the two signal to pass to the VSELP encoder (VSE) 252
for the first mobile station (MST) which is encoded into a digitally compressed signal
which is sent to the first mobile station (MS 1) using the IS-136 cellular communications
protocol. The first mobile station decodes the digitally compressed signal using the
VSELP speech decoder (VSD) 254 to an audio voice signal for the listener to hear.
In this way, the user of the first mobile station is only able to listen to the voice
of the louder of the parties on the PSTN 15 and on the second mobile station. Further,
the voice signal from the second mobile station is summed with the voice signal received
from the first mobile station at summer 264 and are encoded by the hybrid device (H)
for delivery to the user on the PSTN 15. In this way, the user on the PSTN 15 can
listener to both of the mobile stations regardless of which one is louder.
[0115] In a third embodiment, as shown in Figure 18, the cordless cellular base station
10 listens for whichever of the two mobile stations is sending the louder signal and
accepts the voice communication from that mobile station. The cordless cellular base
station 10 utilizes a CODEC 250 which is made up of a VSELP speech encoder (VSE) 252
and a VSELP speech decoder (VSD) 250 as known to those of skill in the art. In the
preferred embodiment, a single CODEC 250 is used to encode and decode voice signals
for both mobile stations. In the preferred embodiment, the communication or voice
signals from a first mobile station (MST) are digitally encoded by the VSELP speech
encoder (VSE) 252 and are sent to the cordless cellular base station 10 using the
IS-136 cellular communication protocol. Similarly, the communication or analog voice
signals from a second mobile station (MS2) are digitally encoded by the VSELP speech
encoder (VSE) 252 and are sent to the cordless cellular base station 10 using the
IS-136 cellular communication protocol. A detector 266 determines which of the two
signals is the louder and passes that signal to the VSELP speech decoder (VSD) 254
which is decoded to a voice signal and is sent to the hybrid for the listener on the
PSTN 15 to hear. The signal from the PSTN 15 is sent through the hybrid and to the
VSELP encoder (VSE) 252 where the signal is digitally compressed. The signal from
the VSELP encoder (VSE) 252 is sent to both the first and second mobile station (MS2)
using the IS-136 cellular communications protocol. Once the signal is received at
each of the mobile stations (MS1/MS2), they respectively decode the digitally compressed
signal using the VSELP speech decoder (VSD) 254 to an audio voice signal for the listeners
to hear. In this way, the users of the first and second mobile stations are able to
listen to the voice of the party on the PSTN 15; however, the user of each of the
mobile stations is unable to hear what is being said by the user of the other mobile
station.
Intercom Feature
[0116] If no call is in progress, the cordless cellular base station 10 has an intercom
capability to connect the standby registered mobile stations 12 with each other through
the cordless cellular base station 10. Using Figure 16 as an example of the cordless
cellular base station 10 circuitry, in the intercom feature, two mobile stations 12
are connected to the cordless cellular base station 10, and there is no speech connection
to the PSTN 15. The cordless cellular base station 10 relays the encoded speech data
stream from each mobile station 12 to the other without decoding in the cordless cellular
base station 10. Each mobile station 12 decodes the received encoded speech data from
the other mobile station 12 for the user to hear. Thus, the VSELP processing in the
cordless cellular base station described in association with Figures 16-18 is bypassed
when the intercom feature is used.
Mobile Station Deregistration
[0117] The mobile station 12 sends a Power-Down deregistration (which is an IS-136 message)
to the cordless cellular base station 10 when the power to the mobile station 12 is
turned off. In addition, the mobile station 12 deregisters from the cordless cellular
base station 10 when the cordless cellular base station's signal becomes too weak,
i.e., when the mobile station 12 moves out of the range of the cordless cellular base
station 10 or when the user presses a soft key sequence on the keypad of the mobile
station 12 and forces a deregistration. Upon receipt of any of the deregistration
requests listed above, the cordless cellular base station 10 updates the status of
the mobile station 12 in the registration list (Figure 8) from an "active" or "standby"
status to a dormant status. Further, the cordless cellular base station 10 preferably
informs the cellular network 16, so that the routing of calls for the mobile station
identification number (MIN) to the landline number is disabled. The mobile station
12 may then register with the regional cellular network 16, using measurements of
the received signal strengths for the neighboring cells, as is known to those of skill
in the art.
[0118] In an alternate embodiment, the cordless cellular base station 10 may request that
the mobile station 12 register periodically. In one preferred embodiment, the mobile
station 12 registration period is approximately every five minutes; that is, the mobile
station 12 needs to register with the cordless cellular base station 10 at least every
five minutes to maintain a connection with the cordless cellular base station 10.
If the registration of the mobile station 12 is not detected during the five minute
registration period, the cordless cellular base station 10 automatically deregisters
the mobile station 12, utilizing the deregistration procedure described above.
[0119] As described above, typically, when the mobile station 12 severs contact with the
cordless cellular base station 10, the cordless cellular base station 10 sends a network
forwarding cancellation message to the CCBS VLR to cancel the forwarding of calls
for the mobile station identification number to the landline number associated with
the cordless cellular base station 10. The cordless cellular base station 10 is informed
during the initial authorization message of which types of registration/deregistration
activities that the CCBS VLR wants to be informed. Some examples of types of deregistration
events for which the network may want to be contacted are: when the mobile station
is turned off, i.e., a power down deregistration, when a manual cancellation of the
cordless service mode occurs, i.e., forced deregistration, etc. If one of the specified
deregistration events occur, the cordless cellular base station sends a network cancellation
message to the CCBS VLR. If the cordless cellular base station 10 is unable to complete
the network cancellation of the call forwarding feature on the first attempt, a second
attempt is made. If the second attempt is also unsuccessful, no additional actions
are required of the cordless cellular base station 10. The calls for the mobile station
12, however, will continue to be forwarded to the landline number associated with
the cordless cellular base station 10 until the mobile station 12 registers with the
cellular network 16 which will automatically update its location and will therefore
cancel the old call forwarding message.
Network Forwarding Cancellation
[0120] Typically, when the mobile station severs contact with the cordless cellular base
station 10, the cordless cellular base station 10 sends a network forwarding cancellation
message to the cellular network 16 to cancel the forwarding of calls for the mobile
station identification number to the landline number associated with the cordless
cellular base station 10. As indicated above, the CCBS VLR informs the cordless cellular
base station during the initial authorization message of which types of registration/deregistration
activities that the CCBS VLR would like to be informed.
[0121] When it is appropriate to notify the CCBS VLR of the deregistration of the mobile
station, the network forwarding cancellation procedure as illustrated in Figure 19a
is initiated. The cordless cellular base station (CCBS) 10 calls the remote network
update number (the CCBS 10 tries the Remote Network Update Number 1 first and if it
is busy it tries the Remote Network Update Number 2) in a network contact calling
step (Network Contact Call) 268 via the public switched telephone network 15, to contact
the cellular network (CN) 16. The cellular network 16 upon answering the call sets
up a modem link in step 272. In an authentication step (AUTH) 274, the cordless cellular
base station 10 starts an authorization timer and sends an authentication message
to the cellular network 16 which includes the cordless cellular base station identification
number and a cordless cellular base station authorization count for the landline number.
Further, the authentication message may include the mobile system identification number
for which the call forwarding message is to be canceled. If a mobile system identification
number is not included, the cellular network 16 will cancel the call forwarding for
all of the mobile stations currently registered with the cordless cellular base station
10. The cordless cellular base station authorization count maintains a running score
of the number of updates the cordless cellular base station 10 has made over this
landline number as a fraud prevention mechanism. The cellular network 16 compares
the call number ID (CNI) from the PSTN for the landline number of the cordless cellular
base station 10 which made the call with the landline number for the cordless cellular
base station 10 stored in a data base on the cellular network 16. In addition, the
cellular network 16 verifies that the mobile system identification number to be updated,
if included, the cordless cellular base station identification number and a cordless
cellular base station authorization count provided by the cordless cellular base station
10 match the stored values in the cellular network 16. Once the authentication message
is processed and validated, a return result message is sent to the cordless cellular
base station 10 in step 276 and the cordless cellular base station 10 authorization
count is updated. Further, the cellular network 16 sets a message receive timer to
see if the cordless cellular base station 10 is going to send it a message. If the
authentication message cannot be validated, i.e., if any of the above-referenced values
do not match, the cellular network breaks the modem connection, releases the call,
and exits the procedure.
[0122] In the meantime, the cordless cellular base station 10 is waiting to receive the
return result message from the cellular network 16. If the return result message is
not received during the authentication timer period or if an error result is received,
the cordless cellular base station will process the error and may attempt a new connection
with the cellular network 16 after a specified period of time has elapsed.
[0123] After receiving the return result message, the cordless cellular base station 10
stops the authentication timer, starts a message receive timer and sends a network
cancellation message to the cellular network 16 to cancel the forwarding of calls
to the cordless cellular base station in step 278 via a modem link. In a preferred
embodiment, the network cancellation message comprises at least the landline number
to which the cordless cellular base station 10 is connected. In addition, the network
cancellation message may include the mobile system identification number for the mobile
station to which the call forwarding cancellation is to apply. If the mobile station
identification number is not provided, the cellular network 16 cancels the call forwarding
feature for all mobile stations which are serviced by the cordless cellular base station
10 that is connected to the designated landline. The cellular network 16 receives
the network cancellation message from the cordless cellular base station 10, verifies
that it agrees with the stored parameters in the cellular network 16, and stops the
message receive timer. If parameters received from the cordless cellular base station
10 do not agree with the stored parameters in the cellular network 16, the cellular
network 16 sends an error message to the cordless cellular base station 10 and resets
the message receive timer. If the message receive timer expires and no message has
been received from the cordless cellular base station 10, the network 16 resends the
return result message, resets the message receive timer, and waits for a response.
If after two timeouts, no message has been received from the cordless cellular base
station 10, the network 16 breaks the modem connection, releases the call, and exits
the procedure. If the parameters received from the cordless cellular base station
10 agree with the stored parameters in the cellular network 16, the cellular network
16 updates the information stored in the cordless cellular base station visitor location
register (CCBS VLR) regarding the location of the mobile station and sends a return
result message in step 280 to the cordless cellular base station 10 over the modem
link to verify the receipt of the information.
[0124] In the meantime, the cordless cellular base station 10 is waiting to receive the
return result message from the cellular network 16. If the return result message is
not received during the message receive timer period or if an error result is received,
the cordless cellular base station 10 will process the error and may attempt to resend
the location update message after a specified period of time has passed. Once the
return result message has been received by the cordless cellular base station 10,
the message receive timer is stopped. The cellular network ends the call forwarding
cancellation procedure and either the cellular network 16 or the cordless cellular
base station 10 releases the call (Release call) in step 286.
[0125] Figure 19b illustrates an alternate embodiment of the network forwarding cancellation
procedure, which is the same as the procedure in Figure 19a from steps 268-278. After
the network cancellation message is received, the information in the message has been
compared with the stored parameters and matches, and the network updates the information
regarding the location of the mobile station, the cellular network checks to see if
it needs to send an updated authorization message to the cordless cellular base station
10. If the cellular network needs to send an authorization message, instead of sending
the return result message as in Figure 19a, the cellular network 16 sends the cordless
cellular base station authorization message in step 282, which includes the cordless
cellular base station identification number and a list of operational frequencies,
which is the same as the initial authorization message described above, and sets a
return result timer. If the message receive timer expires and no message has been
received from the cellular network 16, cordless cellular base station 10 resends the
network cancellation message, resets the timer, and waits for a response. If after
two timeouts, no message has been received from the network 16, the cordless cellular
base station 10 breaks the modem connection, releases the call, and exits the procedure.
If an invalid authorization message is received, the cordless cellular base station
10 sends an authorization error message to the cellular network 16, resets the timer,
and may wait for the receipt of a new authorization message.
[0126] If a valid authorization message is received by the cordless cellular base station
10 in step 282 over the modem link, the cordless cellular base station 10 updates
its operational parameters as received in the message and stops the authorization
timer. The cellular network 16 is able to revoke the cordless cellular base station's
operational authority or update the operational parameters of the cordless cellular
base station 10 with the cordless cellular base station authorization message. The
cordless cellular base station 10 confirms the receipt of message by sending a return
result message to the cellular network 16 in step 284. If the cellular network 16
does not receive the return result message before its return result timer expires,
the cellular network 16 the CCBS authorization message, resets the return result timer,
and waits for a response. If after two timeouts no message has been received from
the cordless cellular base station 10, the cellular network 16 cancels the call forwarding
update, breaks the modem connection, releases the call, and exits the procedure. If
the return result message is received, the cellular network ends the call forwarding
cancellation procedure and either the cellular network 16 or the cordless cellular
base station 10 releases the call (Release call) in step 286.
[0127] After the call forwarding cancellation process is complete, the cellular network
16 no longer routes all calls for the mobile station identification number of the
registered mobile station 12 to the landline number associated with the cordless cellular
base station 10. The procedure for how the cancellation is updated within the cellular
network is similar to the process described in association with Figures 1 9a and 19b
above for the initiation of the call forwarding except that the CCBS VLR 228 revokes
its location change request from the HLR 224, and it lets the HLR 224 handle all of
the requests for the mobile station 12.
Interference Measurement and Avoidance
General Overview of Procedure
[0128] Referring back to Figures 1 and 2, the cordless cellular base station 10 is designed
to operate in the residential home or office environment. This environment can be
potentially very noisy because potentially no dedicated frequency spectrum is allocated
for the cordless cellular base station operation coupled with the fact that the CCBS
frequency usage is not explicitly coordinated with the regional cellular network's
frequency use. The cordless cellular base station 10 has to co-exist in the same cellular
band used by the regional cellular network 16 and views the regional cellular network
16 as a source of background interference. The cordless cellular base station 10 attempts
to avoid the potential interference by the cellular network 16 by choosing frequencies
which, as far as the cordless cellular base station 10 can determine, are not being
used by nearby regional cells 18 or by other nearby cordless cellular base stations
10.
[0129] Since the regional cellular network 16 is unaware of the operating frequency of the
cordless cellular base station 10, it is likely that this system will occasionally
assign voice or control traffic to a channel on which the cordless cellular base station
is operating. Further, it is possible that another cordless cellular base station
10 located close by could be using the same frequency. When such a "collision" between
the cordless cellular base station 10 and a regional cellular network 16 happens,
priority is given to the regional cellular base station 18.
[0130] Preferably, the cordless cellular base station 10 implements a channel selection
algorithm using software instructions, which are stored in the memory of the cordless
cellular base station 10. The processor of the cordless cellular base station preferably
operates on the instructions to implement the channel selection algorithm. Since the
uplink and downlink channels are assigned in pairs, it is not necessary to constantly
monitor both the uplink and downlink frequencies of each pair to determine if the
pair is clear. The channel selection algorithm of the preferred embodiment scans the
downlink frequencies in the cellular band and determines the best and the next-best
downlink cellular frequencies for cordless operation at all times, as described in
more detail below. In brief, the cordless cellular base station 10 periodically measures
received signal strength (RSS) for each of the authorized downlink frequencies of
the cordless cellular base station 10. In addition, the cordless cellular base station
takes RSS measurements on the current uplink operational frequency. Finally, when
a call is in progress, the cordless cellular base station also makes uplink word error
rate (WER) measurements. All of these measurements are known to those of skill in
the art. Under certain conditions, the above measurements may also be made by the
mobile stations using the IS-136 MAHO measurement capabilities known to those of skill
in the art. The mobile station 12 then relays its measurements to the cordless cellular
base station 10. The cordless cellular base station 10 translates the RSS and WER
measurements into a score increment or decrement value based upon a stored score increment
table. After each measurement, the current score increment/decrement value is added
to the previous score value. The score for a frequency is a measure of the amount
of interference encountered on that frequency, with a higher score representing more
interference, and a lower score representing lower interference. In the absence of
interference, the score value will gradually decay towards zero as more measurements
are made. In addition, when frequencies are found to have significant interference,
they are quickly removed from consideration and are only reconsidered after some significant
quiet period in accordance with the scoring mechanism and thresholds described in
more detail herein.
[0131] The cordless cellular base station 10 uses the interference score measurements in
making the choice of an operating frequency. By selecting a frequency from those with
the lowest interference scores, and by using appropriate channel abandonment thresholds
described below, the cordless cellular base station 10 attempts to avoid transmitting
on any frequency which is already in use by the public cellular network 16 or by other
cordless cellular base stations 10 within range. Preferably, the cordless cellular
base station selects for its initial operational frequency the frequency with the
lowest interference score. The cordless cellular base station 10 selects for its backup
frequencies a specified number of downlink frequencies whose scores are below a high
threshold value (Ht). Preferably, depending upon whether a call is in progress or
if a primary mobile station is registered, if the interference score of the current
operational frequency rises above a first low threshold (Lt) or above the high threshold
(Ht), the cordless cellular base station 10 automatically switches its operational
frequency to the first backup frequency as described in more detail below. The cordless
cellular base station 10 also removes backup frequencies from the back-up frequency
list if the interference score rises above the high threshold (Ht). The cordless cellular
base station needs to locate a specified number of downlink frequencies (referred
to herein as M) having score values below the high threshold value (Ht). If a sufficient
number of frequencies are not available, i.e., less than M frequencies are available,
the cordless cellular base station 10 notifies the cellular network 16 of the problem.
In one embodiment, the cellular network will provide the cordless cellular base station
with a list of alternative frequencies for operation. In another embodiment, the cellular
network 16 will temporarily disable the cordless cellular base station 10 for a specified
period of time and then will enable its operation on the same frequencies which are
hopefully free from interference at this later time. The remainder of the interference
measurement procedure is described in more detail below.
Interference Measurement
[0132] The cordless cellular base station 10 has a variety of different modes of operation
that affect the number and type of interference measurements that are performed. In
the basic operational mode when the cordless cellular base station 10 is authorized
for use and none of its registered mobile stations 12 are processing a call, i.e.,
are in an active state, the cordless cellular base station 10 performs an interference
measurement during time slot 4 (40) of the cordless cellular base station transmit
time frame 36. Referring to Figure 4, if either zero or one call is being processed
by the cordless cellular base station 10, the receiver will be silent on timeslot
5 (41) of the receive time frame 35 because the mobile station will not be sending
voice information for the digital traffic channel of the second mobile station (DT2).
Further, the transmitter does not transmit any information on timeslot 4 (40) of the
transmit time frame 36, the cordless cellular base station 10 will not be generating
any of its own interference and thus can make an accurate measurement of the interference
generated by its environment. When the cordless cellular base station 10 measures
the interference on its own operating frequency, the strength of the interference
received on the receiver is measured when no transmission is specifically broadcast
to the receiver of the cordless cellular base station, as known to those of skill
in the art.
[0133] When the cordless cellular base station 10 measures activity on a downlink frequency
other than the operating frequency, the received signal strength (RSS) in dBm is the
noise plus interference power (NPIP). The cordless cellular base station 10 can measure
signal strength on the downlink operating frequency, i.e., the frequency used by the
cellular base station to communicate with the mobile station 12, during the cordless
cellular base station's silent transmission period in Time Slot 4 (40) of the TDMA
transmission frame 36. If fewer than two mobile stations 12 are active, the cordless
cellular base station 10 measures the receive signal strength on the uplink operating
frequency, i.e., the frequency used by the cellular base station to communicate with
the mobile station 12, during unused time slots as described in more detail below.
[0134] When the cordless cellular base station 10 measures signal strength and word error
rate (WER) in a digital traffic channel (DTC) time slot on the uplink operating frequency,
the RSS includes both the desired signal and the noise and interference. For these
measurements, the cordless cellular base station 10 first converts the measured word
error rate (WER) into an equivalent signal to noise-plus-interference ratio (SNIR),
using the conversation factors known to those of skill in the art. Once the SNIR has
been determined, the cordless cellular base station 10 estimates the noise-plus-interference
signal strength as:

   where RSS is the total received power.
The measurement result is expressed as a power equivalent (in dBm) of the noise plus
interference (NPIP) value.
Interference Measurements in Various Modes of Operation
[0135] As indicated above, the cordless cellular base station 10 has several different modes
of operation that affect the number and type of measurements that can be performed.
Each of the modes of operation and the types of measurements made in each mode are
described in more detail in the subsections below. In addition, all of the modes of
operation and the types of measurements which can be performed in each mode are summarized
in Table 1 below.
TABLE 1:
Cordless Cellular Base Station Measurement Modes |
Cordless Cellular Base Station Mode |
Measurements Made By: |
|
cordless cellular base station |
mobile station |
Silent, prior to receipt of a list of allowed frequencies |
none |
none |
Silent, with list of allowed frequencies |
downlink RSS on all authorized frequencies; fast measurement |
none |
DCCH only, no mobile station present or mobile staiton in standby |
downlink RSS on all authorized frequencies and uplink RSS on f0 |
none |
DTC, one mobile station call-connected |
optional downlink RSS on all authorized frequencies, uplink RSS on f0 only uplink WER |
MAHO, downlink WER |
DTC, two mobile stations call-connected |
uplink WER only |
MAHO, downlink WER |
Cordless Cellular Base Station Measurements In Silent Mode
[0136] The silent mode encompasses all states in which the cordless cellular base station's
transmitter is turned off. The cordless cellular base station's transmitter is turned
off for a number of reasons: (1) the cordless cellular base station 10 has not received
network authorization to transmit; (2) transmit authorization has been received, but
there are an insufficient number of acceptable operating frequencies, i.e., frequencies
with interference scores below Ht; (3) the cordless cellular base station 10 has found
an insufficient number of initially acceptable operating frequencies when it abandoned
its last operating frequency; or (4) transmit authorization has been revoked.
Silent Mode Prior to Receipt of a List of Authorized Frequencies
[0137] In silent mode, prior to the receipt of a list of authorized frequencies from the
cellular network during the initial authorization procedure, the cordless cellular
base station 10 is not required to make interference measurements. In addition, since
the list of authorized frequencies has not been received, no mobile stations 12 have
been allowed to register with the cordless cellular base station 10, so no mobile
stations 12 have to report any measurements either.
Silent Mode After Receipt of a List of Authorized Frequencies
[0138] After the receipt of a list of authorized frequencies, the cordless cellular base
station 10 may for a period of time have an insufficient number of acceptable clear
channels so the transmitter is silent. In another case, the cordless cellular base
station 10 may have an insufficient number of acceptable channels when it abandoned
its last operating frequency and is temporarily silent. Without at least one clear
channel, the cordless cellular base station 10 cannot communicate with any of the
mobile stations so the cordless cellular base station has no phone related transmission
or reception duties. Therefore, the cordless cellular base station can make interference
measurements on all of the time slots 1-6. Because additional time slots are available
for making interference measurements, the cordless cellular base station is referred
to as being in a fast interference measurement mode. In the fast interference measurement
mode, the measurement rate is expected to be substantially higher than one measurement
per TDMA frame. Further, in this mode the cordless cellular base station only measures
the down link frequencies so it can establish a sufficient number of clear channels
below the Ht threshold. In a preferred embodiment, the cordless cellular base station
should have M channels with interference scores below Ht before initial operation
can begin. Once the cordless cellular base station finds a sufficient number of clear
channels with scores below the Ht threshold, the cordless cellular base station preferably
selects the frequency with the lowest interference score to be the downlink operating
frequency and starts broadcasting its DCCH on this frequency. At this point, the cordless
cellular base station moves into its authorized mode.
Cordless Cellular Base Station Measurements in Authorized Mode
[0139] On receipt of authorization to transmit, the cordless cellular base station 10 first
notes the list of allowed frequencies given in the authorization transaction. Interference
measurements are restricted to this set of allowed frequencies. Note that this list
could include all frequencies in the cellular frequency range.
[0140] When the cordless cellular base station 10 is authorized for operation (transmitting
a DCCH), the cordless cellular base station 10 makes several types of measurements,
depending on the operating mode.
No Mobile Stations in Active Mode
[0141] When no mobile stations 12 are active, the cordless cellular base station 10 makes
downlink RSS measurements for all of the authorized downlink frequencies using the
scheme described below and uplink RSS measurements for the current uplink frequency
only. When no mobile stations 12 are in an active mode, the cordless cellular base
station 10 is transmitting its half-rate digital control channel on time slot 1, there
are no required transmissions on time slots 2, 3, 5, and 6 besides idle codes because
there is no call in progress to send voice information for DTC1 or DTC2. Further,
as described above the cordless cellular base station 10 will normally be silent during
Time Slot 4 and during this silence in time slot 4 of the transmission frame, at a
time when neither the transmitter nor the receiver is in use, the cordless cellular
base station 10 will make interference measurements, as described below.
[0142] Preferably, the cordless cellular base station 10 nominally makes one downlink interference
measurement in time slot 4 per TDMA frame. The downlink frequency to be measured are
chosen as follows: (1) in 50% of the 40 ms frames in which a measurement is made,
the cordless cellular base station 10 measures the current downlink operating frequency;
(2) in 25% of the 40 ms frames in which a measurement is made, the cordless cellular
base station 10 measures one of the three downlink backup frequencies; (3) in 20%
of the 40 ms frames in which a measurement is made, the cordless cellular base station
10 measures one of the other allowed downlink frequencies whose score is below the
low threshold (Lt); (4) in 5% of the 40 ms frames in which a measurement is made,
the cordless cellular base station 10 measures one of the other allowed downlink frequencies
whose score is at or above the low threshold (Lt).
[0143] When the downlink operating frequency is measured, the estimated noise plus interference
is correlated with all other estimates of noise plus interference on the operating
frequency available for this 40 ms TDMA frame. The largest interference estimate is
used, and any others are ignored. The cordless cellular base station 10 scores this
frequency, as discussed below.
[0144] The uplink RSS measurements are made as follows. Since no mobile stations are active
on receive time slots 2, 3, 5 and 6, the cordless cellular base station 10 measures
uplink RSS at least once per frame in one of these time slots. The RSS measurement
is used as an estimated noise-plus-interference signal strength on the operating frequency.
This estimate is compared with other estimates of the noise plus interference on the
operating frequency and the largest interference estimate is determined. The cordless
cellular base station 10 scores this frequency, as discussed below.
One Mobile Station in Active Mode
[0145] In one embodiment, when one mobile station 12 is active, the cordless cellular base
station 10 makes uplink RSS and WER measurements for the current uplink frequency
only and the mobile station 12 makes downlink WER measurements and forwards them to
the cordless cellular base station. In the preferred embodiment, the cordless cellular
base station also makes downlink RSS measurements of all of the authorized downlink
frequencies using the scheme described below. However, in other embodiments, the cordless
cellular base station may not make downlink RSS measurements.
[0146] The cordless cellular base station 10 nominally makes one downlink RSS interference
measurement on time slot 4 per TDMA frame. The downlink frequency to be measured is
chosen as follows: (1) in 50% of the 40 ms frames in which a measurement is made,
the cordless cellular base station 10 measures the current downlink operating frequency;
(2) in 25% of the 40 ms frames in which a measurement is made, the cordless cellular
base station 10 measures one of the three backup downlink frequencies; (3) in 20%
of the 40 ms frames in which a measurement is made, the cordless cellular base station
10 measures one of the other allowed downlink frequencies whose score is below Lt;
(4) in 5% of the 40 ms frames in which a measurement is made, the cordless cellular
base station 10 measures one of the other allowed downlink frequencies whose score
is at or above Lt.
[0147] When the downlink operating frequency is measured, the estimated noise plus interference
is correlated with all other estimates of noise plus interference on the operating
frequency available for this 40 ms TDMA frame. The largest interference estimate is
used, and any others are ignored. The cordless cellular base station 10 scores this
frequency, as discussed below.
[0148] When one mobile station 12 is active, the CCBS establishes the digital traffic channel
on receive time slots 3 and 6, i.e., DTC1. However, time slots 2 and 5 are still unused,
therefore the cordless cellular base station 10 may attempt to measure uplink RSS
at least once per frame in one of these available time slots. Preferably, the uplink
RSS measurement is made during the receive time slot 5 as it is most likely not to
receive interference from the transmission of the DCCH of the cordless cellular base
station. The RSS measurement is used as an estimated noise-plus-interference signal
strength on the operating frequency. This estimate is compared with other estimates
of the noise plus interference on the operating frequency and the largest interference
estimate is determined.
[0149] Besides measuring the RSS uplink information, the cordless cellular base station
10 also measures the uplink WER for the Digital Traffic Channel (DTC) being received
from that mobile station 12 at least once, and more preferably twice, per 40 ms TDMA
frame. The uplink WER and uplink RSS measurements are combined per the equation described
above to achieve an uplink noise plus interference measurement for the operating frequency.
This estimate is compared with all other estimates of noise plus interference available
for this 40 ms TDMA frame (for example signal quality reports from the mobile) and
the largest interference estimate is determined. The cordless cellular base station
10 scores this frequency, as discussed below.
[0150] When one of the cordless cellular base station's mobile stations is in the active
mode, the mobile station, in compliance with IS-136, will be making downlink MAHO
RSS and WER interference measurements of its own since the CCBS will command it to
do so. The cordless cellular base station 10 receives these measurements from the
mobile station 12 and scores them as discussed below.
[0151] In order to ensure that proper communication is maintained with the mobile station
12, besides receiving interference measurement scores from the mobile station 12,
the cordless cellular base station 10 updates the mobile's MAHO neighbor list each
two to ten seconds. Preferably, the mobile's MAHO neighbor list is updated every five
seconds. As specified in the IS-136 standard, the digital control channel DCCH from
a base station to a mobile station 12 can send control information using o ne of two
control channel formats, the fast associated control channel (FACCH) and the slow
associated control channel (SACCH) formats.
[0152] The SACCH format uses a concatenated set of 12-bit fields from multiple TDMA bursts
to transmit control information during the normal DTC. The FACCH format is used when
the control information is longer and cannot wait for the next DTC time slot to send
the balance of the message. Since the FACCH message steals voice capacity from the
digital traffic channel, it is preferable to wait to send the FACCH message until
there is a detectable silence in the conversation on the digital traffic channel so
the users will not detect the interruption during which the FACCH message is sent.
The neighbor list update is sent using the FACCH, therefore the cordless cellular
base station 10 is required to detect voice activity (possibly based on the RO level
of the VSELP codec) to determine when a quiet period has occurred during the conversation
to send the neighbor list update message for minimum degradation of voice quality.
The neighbor list update message is preferably sent at the first opportunity (i.e.,
when silence in the voice signal from the cordless cellular base station 10 to the
mobile is detected) after the MAHO report from the previous list has been received.
If there is no opportunity within ten seconds, the cordless cellular base station
10 sends the neighbor list update message regardless.
[0153] As per the IS-136 standard, the MAHO neighbor list preferably comprises up to twenty-four
downlink frequencies. In the case of the cordless cellular base station, the twelve
downlink frequencies are chosen from the list of authorized downlink frequencies assigned
to the cordless cellular base station. In the preferred embodiment, the twelve downlink
frequencies comprise the three backup frequencies selected by the cordless cellular
base station, plus nine from the remaining authorized downlink frequencies for the
cordless cellular base station. Preferably, seven of the nine frequencies are selected
among the frequencies whose score is below Lt. If there are fewer than seven such
frequencies, the cordless cellular base station 10 includes all the frequencies whose
interference scores are below Lt. The balance of the nine frequencies are selected
from among the remaining frequencies, other than the current operating frequency.
Two Mobile Stations in Active Mode
[0154] With two mobile stations 12 connected to a call (two DTCs in use), the cordless cellular
base station 10 cannot measure signal strength during Time Slot 4 of the CCBS transmit
frame. This is because time slot 5 of the CCBS receive frame occurs at the same time
as transmit time slot 4, and the cordless cellular base station's receiver is used
during the receive frame time slot 5 as part of the second digital traffic channel
(DTC2) for the second mobile station 12. In this mode, the cordless cellular base
station can only monitor the uplink WER and RSS for each of the mobile stations. Thus,
the cordless cellular base station 10 must rely on the downlink RSS MAHO measurements
and the downlink WER measurements from the two mobile stations 12, which necessarily
excludes the measurement of the current operating frequency of each of the mobile
stations. Thus the cordless cellular base station 10 loses the ability to measure
the RSS of interference on the operating frequency, unless the interference is large
enough to affect the word error rates (WERs).
[0155] Thus, in compliance with IS-136, both of the mobile stations will be making MAHO
downlink RSS and downlink WER interference measurements of their own. The cordless
cellular base station 10 receives these measurements from either one of the mobile
stations 12 and scores the measurements as discussed below.
[0156] With two mobile stations 12 in an active state,. the only measurement that the cordless
cellular base station 10 can make itself is the uplink WER and RSS measurements for
each of the digital traffic channels (DTC) of the mobile stations 12. The uplink WER
measurement is made twice per 40 ms TDMA frame per digital traffic channel (DTC).
The uplink WER measurements from the cordless cellular base station 10 is combined
with the downlink RSS MAHO measurement and the downlink WER measurement made by one
of the mobile stations and used as a measurement of downlink noise plus interference.
The cordless cellular base station 10 scores this frequency, as discussed below.
Score Determination
[0157] In the preferred embodiment, the interference measurements are translated into a
score increment or decrement. The interference score for each frequency can preferably
range from O to 2
22-1. In addition, the CCBS VLR provides the cordless cellular base station 10 with
the initial score value for each of the operational frequencies in the authorization
message that is sent by the cellular network 16. In another embodiment, the initial
score value is set to be a default value when the CCBS is manufactured. In a preferred
embodiment, on power-up or reset, the cordless cellular base station 10 initializes
the frequency scores to a value equivalent to the 1 high threshold (Ht)+7500. This
makes these frequencies initially unacceptable for use but available if they stay
clear for 5 minutes, which is equivalent to 7500 40 ms TDMA frames. On subsequent
receipt of a new list of allowed frequencies, the cordless cellular base station 10
initializes scores on any frequencies that were not previously allowed to Ht+7500.
In another embodiment, certain of the new frequencies on the allowed frequency list
may be sent with preassigned initial values. The frequencies which are sent with preassigned
initial values will override the initial value set at the time of manufacturing or
previously provided by the CCBS VLR
[0158] The cordless cellular base station 10 takes the interference measurement for each
frequency which is expressed as a power equivalent (in dBm) of the noise plus interference
and translates the measured noise plus interference power level into a score increment
or decrement using a staircase function 288 in Figure 20. The cordless cellular base
station 10 determines between which X values the interference measurement occurs and
reads the appropriate decrement or increment value from the Y axis.
[0159] As indicated below in the preferred embodiment the X values for a mobile station
measurement are different from the X values for the cordless cellular base station
measurement. The reason for this difference is that the mobile station 12 will be
able to move from inside the home or office environment to outside of the home or
office environment and it is believed that it will be subject to a slightly elevated
level of interference because of its ability to be located outside. The cordless cellular
base station 10, on the other hand, is stationary and will remain inside where it
is believed that it will be subjected to less interference. To reconcile this difference,
less interference detected by the cordless cellular base station 10 is required to
make a larger jump in the interference score. For example, in the preferred embodiment,
a -90 dBm measurement by the cordless cellular base station 10 would result in an
interference score at the Y
3 level, whereas -90 dBm measurement by the mobile station 12 would result in an interference
score at the Y
2 level.
The preferred X values for Figure 20 are shown in Table 2 below:
TABLE 2:
Preferred 'X' Coordinate Values for the Staircase Function |
|
mobile station |
cordless cellular base station |
X1 |
-112 dBm |
Nfloor+6 dBm |
X2 |
-95 dBm |
-100 dBm |
X3 |
-85 dBm |
-90 dBm |
[0160] As shown in the table, the value for X
1 for the cordless cellular base station is set at 6 dBm above the receiver's noise
floor. In the preferred embodiment, the receiver's noise floor is -118 dBm, thus the
preferred value for X
1 for the cordless cellular base station is-112 dBm.
The preferred Y values for Figure 20 are shown in Table 3 below:
TABLE 3:
Preferred 'Y' Coordinate Values for the Staircase Function |
|
1 measurement
per TDMA
frame |
1 measurement
per TDMA frame |
Y0 |
-1 |
-N |
Y2 |
Ymax/50 |
Ymax/50 |
Y3 |
Ymax/2 |
Ymax/2 |
where Y
max is the full-scale (saturation) value of the score. In the preferred embodiment, Y
max is 2
22-1. When an mobile station 12 is present and in active (conversation) mode, the value
of N in this table is replaced by N/2. In effect, this gives the cordless cellular
base station 10 and mobile station 12 measurements each half of the total weight.
[0161] As shown in the preferred Y value table, the values of Y
0 and Y
2 are proportional to the interval between successive measurements on the frequency
in question. This normalizes the measurements, making the decay rate for a score on
a clear frequency independent of the measurement rate. For example, once a particular
score reaches the saturation value, removal of the interference will cause the score
to decay to zero in 2
22-1 times 40 ms; about 2 days. The values of X
1, X
2, X
3, Y
0, Y
2, and Y
3, as well as the number of steps in the staircase function 288, are the currently
preferred values. It is contemplated that these values would be changed depending
upon the actual use of the system in order to maintain the goals of quickly removing
frequencies from consideration when they are found to have significant interference
and only reconsider new frequencies after some significant quiet period.
[0162] The cordless cellular base station 10 adds the increment or decrement value read
from the Y axis to the previous interference score for the measured frequency. The
increment values of the Y axis were chosen such that interference above the X
3 value will cause a large jump in the interference score and will quickly make this
channel undesirable for use as either a backup frequency or an operating frequency.
Whereas, interference between the X
3 value and the X
2 value will cause a medium size jump in the interference score which should make it
undesirable for use as an operating frequency, but could make it useable as a backup
frequency depending upon how persistent this level of interference is. Interference
between the X
2 value and the X
1 will not change the present score value, so the channel will remain in its current
use level. Interference below the X
1 value will enable the interference score to be decremented, thus making it more desirable
for use as a potential backup or operational frequency. The increment and decrement
values were chosen such that continual interference measurements on the same frequency
causes the score to increase rapidly to quickly alert the cordless cellular base station
10 of the interference. Further, occasional interference which is bursty in nature,
i.e., sometimes detected on the channel sometimes not detected on the channel, causes
the score to increase more slowly but if persistent it eventually can lead to the
channel scoring unacceptably high. Finally, when there is little or no interference,
i.e., below the X
1 value, a decrement allows the score to slowly decay toward zero.
Score Storage
[0163] The cordless cellular base station 10 stores the scores for each of the operational
frequencies in a data base, such as the date base shown in Table 4 below. The cordless
cellular base station 10 normalizes the score increments and decrements according
to the interval between measurements. Therefore, the table below also stores the number
of TDMA frames which have occurred between measurements to normalize the interference
scores as described in more detail below. In a preferred embodiment, the cordless
cellular base station 10 is able to operate on any of the available four hundred sixteen
"A" side or "B" side pairs of uplink and downlink frequencies in the cellular frequency
bands. In one embodiment, as described above, the cellular network 16 offers the cordless
cellular base station 10 a list, or range of frequencies, carved out of the cellular
frequency bands within which to operate. To efficiently use the measurement capabilities
of the cordless cellular base station 10 and its mobile stations 12, the cordless
cellular base station 10, once authorized by the cellular network 16 with such a frequency
list supplied, does not update or otherwise maintain the scores of frequencies which
are not on the network-supplied list of frequencies that the cordless cellular base
station 10 is enabled to use.
TABLE 4:
Interference Scores Maintained by Cordless Cellular Base Station |
Frequency |
Interference Score |
Number N of TDMA frames since the last measurement by: |
|
|
Cordless Cellular Base Station |
Mobile Station 1 |
Mobile Station 2 |
1 |
|
|
|
|
2 |
|
|
|
|
3 |
|
|
|
|
... |
|
|
|
|
416 |
|
|
|
|
Normalizing Measurements
[0164] Since measurement rates are not uniform over time, the cordless cellular base station
10 must normalize the score increments and decrements according to the interval between
measurements. The score updating process requires the cordless cellular base station
10 to track the update rate. The update rate is expressed as the number N of 40 ms
TDMA frames since the last interference measurements on any given frequency. Any one
frequency may have different update rates from different measurement sources. The
range of possible values for N is limited depending upon the measurement mode, as
described below.
[0165] The value of N will, in general, be different for measurements made by the cordless
cellular base station 10, the first mobile station 12, and the second mobile station
12. The value of N depends on the measurement mode, and can be calculated as indicated
in Table 5 below. The following abbreviations are used in the table: (1) f
ou is the operating downlink frequency; (2) f
od is the operating uplink frequency; (3) f
1, f
2 and f
3 are the three backup frequencies; (4) n
b is the number of backup frequencies; (5) n
low is the number of allowed frequencies other than f
0-f
3 which have scores less than Lt; and (6) n
high is the number of allowed frequencies other than f
0-f
3 which have scores greater than or equal to Lt.
TABLE 5:
Preferred Interference Measurement Rates |
Cordless
cellular base
station mode |
Number N of TDMA frames
since the last measurement |
|
Cordless Cellular
Base Station |
Mobile Station 1 |
Mobile Station 2 |
Silent, with a list of allowed frequencies |
416/6 |
no measurements |
no measurements |
DCCH only, no mobile stations present or mobile stations in standby |
fod:2/0.875
fou:0.5
f1-3:4nb0.875
<Lt:5nlow/0.875
> Lt:20nhigh//0.8.75 |
no measurements |
no measurements |
DTC, mobile station 1 active, mobile station 2 not present or in standby |
fod:2/0.875
fou:1 [measured each frame]
f1-34nb0.875
<Lt:5nlow/0.875
>Lt:20nhigh//0.8.75 |
fod:75
f1-3:75
<Lt:75nlow/7
> Lt:75nhigh/2 |
no measurements |
DTC, two mobile stations active |
fod:no measurements
fou:1 [measured each frame] |
fod:75
f1-3:75
<Lt:75nlow/7
> Lt:75nhigh/2[all measured by one mobile station] |
[0166] For example, consider the measurements made by the cordless cellular base station
10 with one mobile station 12 in active mode (third row, first cell of the above table).
In this example, the cordless cellular base station 10 measures downlink interference
on the operating frequency f
od once every two frames, except that 1 of 8 such measurements is preempted by an idle
code transmission as described above. This pre-emption of downlink measurements accounts
for the divisor 0.875 here and elsewhere in the cordless cellular base station 10
column of the table. With one mobile active, as described above, the cordless cellular
base station 10 measures uplink interference of the operating frequency f
ou once per frame. Since these measurements do not occur in Time Slot 4, they are never
preempted for an idle code transmission, thus N is 1. The cordless cellular base station
10 measures downlink interference on one of the downlink backup frequencies f
1-3 at an average interval of four frames (25 percent of the measurement frames as describe
above). Thus, to measure all the backup frequencies one time requires 4n
b frames, and again the 0.875 divisor must be applied because the measurements are
preempted for the occasional idle code transmission in time slot 4. In 20 percent
of the measurement frames, the cordless cellular base station 10 measures downlink
interference on one of the allowed frequencies with scores below Lt. This means an
average of 5/0.875 frames between non-preempted measurements, or 5n
low/0.875 frames before all these frequencies can be measured once. In 5 percent of the
measurement frames, the cordless cellular base station 10 measures downlink interference
on one of the allowed frequencies with scores equal to or greater than Lt. This means
an average of 20/0.875 frames between non-preempted measurements, or 20n
high/0.875 frames before all these frequencies can be measured once.
[0167] The mobile station's measurements in active (conversation) mode are listed in the
third row, second cell of the above table. These values assume an average of three
seconds (IS-136's allowable range is two to ten seconds) between successive MAHO reports.
The measurements are as follows: One indirect measurement of downlink interference
on the operating frequency every 75 frames (= three seconds) is taken. For this measurement,
the cordless cellular base station 10 combines the mobile station's downlink WER and
downlink RSS results using the equation described above to achieve the noise plus
interference measurement. One direct measurement of downlink interference on each
backup frequency is taken every 75 frames. As described above, all downlink backup
frequencies are on every MAHO list. Every 75 frames, measurements of downlink interference
on seven of the allowed frequencies on the MAHO list with scores below Lt are taken.
This works out to 75n
low/7 frames to measure each of these frequencies once. Every 75 frames, measurements
of downlink interference are taken on two of the allowed frequencies with scores equal
to or greater than Lt. This works out to 75n
low/2 frames to measure each of these frequencies once.
Frequency Selection
[0168] The cordless cellular base station 10 uses its interference scores as the input to
its decisions to select, retain, or abandon an operating frequency or a backup frequency.
Changes in operating or backup frequencies result from the score on the frequency
exceeding a specified threshold. The two thresholds used by the cordless cellular
base station 10 are the high threshold, Ht, and the low threshold, Lt. In the preferred
embodiment, Ht is set to Y
max/2 equal to 2
21, and Lt is set to equal to Y
max/8, equal to 2
19. In one embodiment, the low and high thresholds are set to be equal.
[0169] The cordless cellular base station 10 forms a ranked list of 4M, or four times M,
downlink frequencies with the lowest acceptable interference scores from the above
list of all frequency scores. Only downlink frequencies whose interference scores
are below the High Threshold (Ht) are eligible for inclusion in this list. Therefore,
under some conditions the list will contain fewer than 4M frequencies. In the preferred
embodiment, the cordless cellular base station 10 recompiles this ranked list every
two seconds.
[0170] The cordless cellular base station 10 also maintains an unranked list of all frequencies
with interference scores less than a Low Threshold (Lt). In the preferred embodiment,
the cordless cellular base station 10 recompiles this list at least once every two
seconds.
[0171] Figure 21 shows a simplified example of the interference score 290 for a particular
frequency (note this example does not take into consideration the status of a call
or if a primary mobile station is registered with the cordless cellular base station).
At point A, when the interference score rises above Lt, the cordless cellular base
station 10 would abandon this frequency if this were the operating frequency and if
the other scores were below Lt. At point B, when the interference score rises above
Ht, this frequency is unconditionally rejected for use as either an operating or backup
frequency. At point C, when the interference score decays below Ht, this frequency
once again becomes eligible for selection as a backup or operating frequency.
Initial Selection and Reselection of the Operating Frequency
[0172] The initial downlink operating frequency is preferably the frequency on the authorized
frequency list with the lowest interference score, namely the frequency at the top
of the ranked list. If fewer than M frequencies have scores below Ht, the cordless
cellular base station 10 will preferably not begin transmitting and will alert the
CCBS VLR of the problem.
[0173] Whenever the score of the current downlink operating frequency is updated, the cordless
cellular base station 10 evaluates the new score to decide whether or not to change
the operating frequency. In the preferred embodiment, the rules for changing the operating
frequency also depend upon whether the primary mobile stations are registered or if
a call is in progress. Thus, in the preferred embodiment, if the cordless cellular
base station's primary mobile station 12 is in active or standby mode or if any of
the registered mobile stations are on a call,: the cordless cellular base station
10 will no longer operate on the current operating frequency if: its interference
score equals or exceeds Lt and if the first backup frequency's interference score
is lower than the operating frequency's score. If the cordless cellular base station's
primary mobile station 12 is in the dormant mode, and if no digital traffic channel
(DTC) is active, i.e., none of the registered mobile stations are on a call: the cordless
cellular base station 10 will no longer operate on the current operating frequency
if: its interference score equals or exceeds Ht, otherwise, the cordless cellular
base station will remain on its current operating frequency until the primary mobile
station user registers with the cordless cellular base station or the interference
level exceeds Ht. This feature is provided, so that the primary user's phone can automatically
locate its cordless cellular base station 10 when it comes into proximity with it.
If the cordless cellular base station 10 were frequently changing its operating frequency
when the primary mobile station was not registered, it would be possible for the mobile
station 12 to change frequencies such that the current operational frequency was not
on the list of the operating and backup frequencies that the mobile station 12 stored
when it last registered with the cordless cellular base station 10. Thus, the primary
mobile station would not be able to automatically locate and register with the cordless
cellular base station 10, because it would not be aware of the current operating frequency
of the base station 10, and would therefore not know where to look for its new frequency.
In this situation, the user would need to manually invoke a test registration by the
mobile station.
[0174] If the cordless cellular base station 10 ceases to operate on the current operating
frequency, the replacement operating frequency is the first backup frequency f
1. If a call is active at the time the cordless cellular base station 10 abandons the
operating frequency, the cordless cellular base station 10 preferably performs a handoff
to the new frequency, using a handoff procedure known to those of skill in the art.
However, in a typical handoff the mobile station would be switching from one cell
to another. In the case of a handoff initiated by the cordless cellular base station,
the mobile station remains in the same cell (the cordless cellular base station cell)
and changes its operating frequencies. Since the same radio transceiver remains in
control of the call while switching frequencies, the handoff procedure is carefully
controlled to ensure that the transceiver does not lose the call while it tunes to
the new frequency. If a call is not in progress, the cordless cellular base station
10 will change its operating frequency to the first backup frequency f
1 and will notify the mobile stations 12 listed in standby mode by sending the new
operating frequency in the next neighbor list message as described above.
[0175] If, at the time the cordless cellular base station 10 abandons its operating frequency,
fewer than M frequencies have scores below Ht, the cordless cellular base station
10 preferably contacts the CCBS VLR and informs the CCBS VLR that it does not have
enough clear channels for operation. The CCBS VLR may send the cordless cellular base
station an new set of channels, or may send it a lower M value, or may send the cordless
cellular base station an empty list of authorized frequencies which will cause it
to cease transmission until a new set of authorized frequencies are provided. The
cordless cellular base station 10 will make its own measurements and maintain interference
scores for the newly supplied list of authorized frequencies. Once there are M or
more frequencies with scores below Ht, the cordless cellular base station 10 begins
transmitting on one of the frequencies with an interference score below Ht.
[0176] In an alternate embodiment, at the time the cordless cellular base station 10 abandons
its operating frequency, fewer than M frequencies have scores below Ht, the cordless
cellular base station 10 ceases to transmit its DCCH. The cordless cellular base station
10 will make its own measurements and maintain interference scores, regularly and
frequently checking the number of frequencies whose scores are below Ht. Once there
are M or more frequencies with scores below Ht, the cordless cellular base station
10 randomly chooses a waiting time, uniformly distributed between 0 and 5 minutes.
After this waiting time expires, and provided that there are still M or more frequencies
with scores below Ht, the cordless cellular base station 10 begins transmitting, preferably
on the frequency with the lowest score.
[0177] In order to avoid dropping a call in progress, the cordless cellular base station
10 temporarily sets M=1 while a digital traffic channel (DTC) is in use. When the
call ends (i.e., when neither DTC is in use), the cordless cellular base station 10
will reset M to its true value. If the cordless cellular base station 10 changed its
operating frequency during the call, the cordless cellular base station 10 applies
the following congestion test after the end of the call: If fewer than M frequencies
have scores below Ht, the cordless cellular base station 10 preferably contacts the
CCBS VLR and informs the CCBS VLR that it does not have enough clear channels for
operation. The CCBS VLR may send the cordless cellular base station a new set of channels,
or may send a lower M. value, or may send the cordless cellular base station an empty
list of frequencies which will cause it to cease transmission until a new set of authorized
frequencies are provided.
Initial Selection and Reselection of Backup Frequencies
[0178] For both initial and subsequent selection, the cordless cellular base station 10
chooses each backup frequency equiprobably from the top 2M (two times M) frequencies
in the ranked list of the best acceptable frequencies maintained in the cordless cellular
base station 10 score table. The operating frequency is removed from the ranked list
before the backup frequency is chosen. The reason that the backup frequencies are
equiprobably chosen from the list of possible frequencies rather than being chosen
deterministically is that it prevents two neighboring cordless cellular base stations
from selecting the same set of backup frequencies. If the best interference scores
where chosen, it would be highly likely that two neighboring cordless cellular base
stations would have similarly ranked interference score measurements for similar channels.
If similar backup frequencies were chosen for neighboring cordless cellular base stations,
the chances of the neighboring cordless cellular base stations selecting the same
frequency as their new operation frequency and resulting in the occurrence of a collision
would be very high. By equiprobably choosing the backup frequencies from the list
of suitable frequencies, the chances of two neighboring cordless cellular base stations
having the same set of backup frequency is greatly lessened. Whenever the score of
one of the backup frequencies is updated, the cordless cellular base station 10 evaluates
the new score to decide whether or not to change this backup frequency. If the interference
score of a backup frequency exceeds Ht or exceeds the (4M)-th position in the overall
ranking, the cordless cellular base station 10 replaces this backup frequency.
[0179] When replacing a backup frequency, the cordless cellular base station 10 maintains
the ordering of the backup frequency list {f
1, f
2, f
3} for proper ordering in the broadcast neighbor list. The replacement backup frequency
becomes f
3. If the old f
3 was not replaced, it becomes f
2. If the old f
2 was not replaced, it becomes f
1.
Example of Score-Based Frequency Selection and Reselection
[0180] The following example described in association with Figure 22 is used to help clarify
the frequency selection concepts. In this example, there are three allowed frequencies,
labeled a, b, and c. In addition, for this example, M is set at two, thus two frequencies
having a score below Ht must be available to enable operation of the cordless cellular
base station and it is assumed that a primary mobile station is registered with the
cordless cellular base station. Figure 22 shows the interference scores for these
three frequencies as a function of time, and the cordless cellular base station's
selection of operating frequency f
0 and backup frequencies f
1 and f
2 as a function of time. Initially frequencies (a) and (b) are acceptable for use.
Since frequency (a) has the lower score, it becomes the operating frequency and (b)
becomes the first backup. At time t
1, frequency (c) becomes acceptable and is added as the second backup.
[0181] At time t
2, the score for the operating frequency (a) exceeds Lt. The first backup frequency
(b), which has a lower score than does frequency (a), becomes the new operating frequency.
The second backup moves up to first position, and the former operating frequency (a)
is chosen as the replacement backup frequency.
[0182] At time t
3, the score for the second backup frequency (a) exceeds Ht and it is therefore removed
from the backup list.
[0183] At time t
4, the score for the operating frequency (b) exceeds Lt and in the preferred embodiment,
the primary mobile station is registered with the cordless cellular base station.
The first backup frequency (c), which has a lower score than does frequency (b), becomes
the new operating frequency. Due to the intermittent or weak nature of the interference,
the interference score for the former operating frequency (b) it still below Ht. Therefore
frequency (b) is chosen as the replacement backup frequency.
[0184] At time t
5, the score for the first backup frequency (b) exceeds Ht and it is therefore removed
from the backup list. This leaves only one frequency with an acceptable score. Although
this would seem to violate the rule that the minimum number of frequencies below Ht
(M) must be at least 2, this constraint is only enforced at the time the cordless
cellular base station 10 changes its operating frequency. For intermittent or weak
interference, the constraint is M-1 acceptable frequencies for continued operation,
versus M acceptable frequencies for initial operation. Thus the cordless cellular
base station 10 continues to transmit at time t
5.
[0185] At time t
6, frequency (a) becomes acceptable and is added as the first backup. At time t
7 frequency (b) becomes acceptable and is added as the second backup.
Quick Start
[0186] The quick start feature enables the cordless cellular base station 10 to quickly
become operable using a few frequencies, referred to as "quick start frequencies",
supplied by the cellular network 16 which are known to be clear channels in the area
where the cordless cellular base station is located. The goal for the use of the quick
start frequencies is to get the cordless cellular base station operating quickly using
these dedicated frequencies and then to migrate them off of these frequencies to other
channels as they are found to be clear. In one embodiment, these cordless cellular
base station downlink frequencies are set aside by the registered cellular network
to permit the use of the cordless cellular base station as a sort of safe haven. In
a preferred embodiment, in the initial authorization message, the cordless cellular
base station 10 is sent two sets of frequencies. The first set is a short list of
frequencies known to be clear by the cellular network 16, referred to as quick start
frequencies," which are provided with a low initial interference score. The second
set is a large set of frequencies with high initial interference scores. Preferably,
the initialization score for the quick start frequencies is at least close to the
high threshold Ht. By starting out with a low initial interference score, the quick
start frequencies will quickly become available for use as an operating frequency
as their score will continue to decrement, since the frequency is clear, until at
least one of the frequencies falls below the high threshold (Ht) and can be used as
the initial operating frequency. In a more preferred embodiment, the initialization
score for the quick start frequencies is below the high threshold Ht, so all of the
quick start frequencies will immediately be available for use as the operating frequency.
In addition to the two sets of frequencies, the cellular network 16 will provide an
initial value M
i, for M, the minimum number of clear channels the cordless cellular base station needs
to operate. In the initial authorization message, M is equal to the number of quick
start frequencies provided. This scheme would be useful in a spectrally congested
are such as a tall building.
[0187] After a specified period of time X, the cellular network 16 will try to migrate the
cordless cellular base station 10 off the quick start frequencies. In the preferred
embodiment, this period of time X will be forty-eight hours. During the next network
update (either a location update or a network cancellation) after the expiration of
X, the cellular network 16 will increase M to M
n, the requirement for the minimum number of clear channels for the cordless cellular
base station to maintain operation. This information is given to the cordless cellular
base station in an authorization message which is sent back from the cellular network
to the cordless cellular base station 10 after the location update or network cancellation
process has been completed as described in more detail above. If the cordless cellular
base station 10 does not have the minimum number of operating frequencies, it will
send an alarm message to the cellular network 16. At this point, the cellular network
will allow the cordless cellular base station 10 to operate with both sets of frequencies
until M
i can be increased to M
n and the cordless cellular base station has enough cellular frequencies for operation.
If the cordless cellular base station 10 has the required number of operating frequencies,
the cellular network may remove the original "quick start frequencies" and allow it
operate on the remaining clear channels. It will remove the "quick start frequencies"
during the next network update exchange using the authorization message. The authorization
message will include only the second set of frequencies, i.e., excluding the "quick
start frequencies," and a new M value equal to M
n-M
i.
Local Frequency Monitor
[0188] As described above, the cordless cellular base station periodically initiates a phone
call to the CCBS VLR. In a preferred embodiment, after initiation of the phone call,
the cordless cellular base station 10 advantageously downloads all of the stored interference
scores measured using the above described algorithm for all of its authorized frequencies.
The CCBS VLR forwards the interference score information to a data collection node
(DCN) in the cellular network.
[0189] In an alternate embodiment, the CCBS VLR periodically sends the cordless cellular
base station a new authorization message with the telephone number for the data collection
node instead of the telephone number for the location update information. The cordless
cellular base station calls the new telephone number and reports the interference
data directly to the data collection node. In one embodiment, after a specified period
of time, during the next network contact between the CCBS and the network, the CCBS
VLR sends the cordless cellular base station a new authorization message to reinstate
the telephone number to report its location update messages. In another embodiment,
the data collection node sends the cordless cellular base station a new authorization
message to reinstate the telephone number of the CCBS VLR to report its location update
messages.
[0190] Advantageously, the cellular network can use these interference scores to assist
in learning about the peak interference periods for the cell containing the CCBS.
Further, the interference scores are useful in assigning or re-assigning the operational
frequencies for the regional cells.
[0191] The present invention may be embodied in other specific forms without departing from
its spirit or essential characteristics. The described embodiments are to be considered
in all respects only as illustrative and not restrictive. The scope of the invention
is, therefore, indicated by the appended claims rather than the foregoing description.
All changes which come within the meaning and range of equivalency of the claims are
to be embraced within their scope.